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THE 

PRINCIPLES    OF    BIOLOGY 


BY 

HERBERT   SPENCER 
w 

AUTHOR    OF    SOCIAL    STATICS,    EDUCATION,    STUDY    OF    SOCIOLOGY, 

ESSAYS  :    SCIENTIFIC,     POLITICAL,    AND    SPECULATIVE, 

FACTORS    OF   ORGANIC    EVOLUTION,    ETC. 


IN   TWO   VOLUMES 
VOL.    I 


NEW     YORK 
APPLETON     AND      COMPANY 
1897 


Copyright,  18G6, 
By  D.   APPLETON  AND  COMPANY. 


QH307 


PREFACE  TO  THE  AMERICAN  EDITION. 


The  System  of  Philosophy  now  in  course  of  publication  by 
Mr.  Herbert  Spencer  begins  with  a  volume  of  First  Princi- 
ples, which  was  republished  in  this  country  a  year  or  two 
since.  The  subject  of  Biology  comes  next  in  order,  and  is  to 
be  treated  in  two  volumes,  of  which  the  present  is  the  first ; 
Volume  II.  will  probably  appear  toward  the  close  of  the  year. 
In  accordance  with  the  author's  plan,  the  doctrine  or  method 
of  Evolution  unfolded  in  First  Principles  and  applied  to  Biol- 
ogy in  the  present  work,  will  be  carried  out  in  the  subsequent 
treatment  of  the  Principles  of  Psychology  and  the  Principles 
of  Sociology. 

In  the  preface  to  the  English  edition,  Mr.  Spencer  remarks  : 

"  The  aim  of  this  work  is  to  set  forth  the  general  truths  of 
Biology,  as  illustrative  of,  and  as  interpreted  by,  the  laws  of 
Evolution  :  the  special  truths  being  introduced  only  so  far  as 
is  needful  for  elucidation  of  the  general  truths. 

"  For  aid  in  executing  it,  I  owe  many  thanks  to  Prof.  Hux- 
ley and  Dr.  Hooker.  They  have  supplied  me  with  informa- 
tion where  my  own  was  deficient ;  and  in  looking  through 
the  proof-sheets,  have  pointed  out  errors  of  detail  into  which 
I  had  fallen.  By  having  kindly  rendered  me  this  valuable 
assistance,  they  must  not,  however,  be  held  committed  to  any 
of  the  enunciated  doctrines  that  are  not  among  the  recog- 
nized truths  of  Biology." 

New  York,  March,  18GG. 


CONTENTS  OF  VOL.  I. 


PART   I.— THE   DATA   OF  BIOLOGY. 

CHAP.  PAGE 

I. — ORGANIC    MATTER              ......  3 

II. — THE    ACTIONS    OF    FORCES    OX    ORGANIC    MATTER         .  25 

III. THE    RE-ACTIONS    OF    ORGANIC    MATTER    ON    FORCES  42 

IV. PROXIMATE    DEFINITION    OF    LIFE    ....  59 

V. THE   CORRESPONDENCE   BETWEEN   LIFE    AXD  ITS  CIR- 
CUMSTANCES             ......  T2 

VI. THE    DEGREE    OF    LIFE    VARIES    AS    THE    DEGREE    OF 

CORRESPONDENCE               .....  82 

VII. THE    SCOPE    OF    BIOLOGY            .....  94 


PART   II.— THE   INDUCTIONS   OF  BIOLOGY. 

I. GROWTH 107 


II. DEVELOPMENT 

III. FUNCTION      . 

IV. — WASTE    AND    REPAIR 

V. ADAPTATION 

VI. INDIVIDUALITY       . 

VII. — GENESIS 


133 

1513 

169 

184 

201 

209 


Vlll 


CONTENTS. 


CHAP. 

VIII. HEREDITY     ..... 

IX. VARIATION 

X. GENESIS,    HEREDITY,    AND    VARIATION 

XI. — CLASSIFICATION  .... 
XII. DISTRIBUTION  .... 


PAGE 

239 
257 
273 
292 
311 


PART  III.— THE   EVOLUTION  OF  LIFE. 

I. PRELIMINARY 331 

II. GENERAL     ASPECTS    OF    THE     SPECIAL-CREATION-HY- 
POTHESIS       .......  333 

III. — GENERAL    ASPECTS    OF    THE    EVOLUTION-HYPOTHESIS  346 

IV. THE    ARGUMENTS    FROM    CLASSIFICATION  .  .356 

V. — THE    ARGUMENTS    FROM    EMBRYOLOGY      .             .             .  365 

VI. — THE    ARGUMENTS    FROM    MORPHOLOGY     .             .             .  380 

VII. THE    ARGUMENTS    FROM    DISTRIBUTION     .      '      .             .  388 

VIII. — HOW    IS    ORGANIC    EVOLUTION    CAUSED?.            .            .  402 

IX. EXTERNAL    FACTORS        .  .  .  .  .  .411 

X. INTERNAL    FACTORS         ......  420 

XL — DIRECT    EQUILIBRATION             .....  432 

XII. INDIRECT    EQUILIBRATION         .....  443 

XIII. THE    CO-OPERATION    OF    THE    FACTORS       .             .             ."  464 

XIV. THE   CONVERGENCE    OF    THE    EVIDENCES              .             .  470 


PART    I. 


THE   DATA   OF   BIOLOGY. 


CHAPTEE  I. 

ORGANIC  MATTER. 

§  1.  Of  tlie  four  chief  elements  which,  in  various  com- 
binations, make  up  living  bodies,  three  are  gaseous.  While 
carbon  is  known  only  as  a  solid,  oxygen,  hydrogen,  and 
nitrogen  habitually  maintain  the  aeriform  state.  Only  by 
intense  pressures  joined  with  extreme  refrigerations  have 
two  out  of  the  three  (some  say  all)  been  reduced  to  the  liquid 
form.  There  is  a  certain  significance  in  this.  When  we 
remember  how  those  re-distributions  of  Matter  and  Motion 
which  constitute  Evolution,  structural  and  functional,  imply 
motions  in  the  units  that  are  re-distributed ;  we  shall  see  a 
probable  meaning  in  the  fact  that  organic  bodies,  which 
exhibit  the  phenomena  of  Evolution  in  so  high  a  degree,  are 
mainly  composed  of  ultimate  units  having  extreme  mobility. 
The  properties  of  substances,  though  destroyed  to  sense  by 
combination,  are  not  destroyed  in  reality  :  it  follows  from  the 
persistence  of  force,  that  the  properties  of  a  compound  are 
resultants  of  the  properties  of  its  components — resultants  in 
which  the  properties  of  the  components  are  severally  in  full 
action,  though  greatly  obscured  by  each  other.  One  of  the 
leading  properties  of  each  substance  is  its  degree  of  molecular 
mobility  ;  and  its  degree  of  molecular  mobility  more  or 
less  sensibly  affects  the  molecular  mobilities  of  the  various 
compounds  into  which  it  enters.  Hence  we  may  infer  some 
relation  between  the  gaseous  form  of  three  out  of  the  four 


WOFERTT  LMAAT 
v   t  State  Collet* 


4  THE   DATA   OF   BIOLOGY. 

chief  organic  elements,  and  that  comparative  readiness  dis- 
played by  organic  matters  to  undergo  those  changes  in  the 
arrangement  of  parts  which  we  call  development,  and  those 
transformations  of  motion  which  we  call  function. 

Considering  them  chemically  instead  of  physically,  it  is 
to  be  remarked  that  three  out  of  these  four  main  components 
of  organic  matter,  have  affinities  which  are  narrow  in  their 
range  and  low  in  their  intensity.  Hydrogen  combines  with 
comparatively  few  other  elements ;  and  such  chemical  energy 
as  it  does  show,  is  scarcely  at  all  shown  within  the  limits  of 
the  organic  temperatures.  Of  carbon  it  may  similarly  be  said 
that  it  is  totally  inert  at  ordinary  heats  ;  that  the  number  of 
substances  with  which  it  unites  is  not  great ;  and  that  in 
most  cases  its  tendency  to  unite  with  them  is  but  feeble. 
Lastly,  this  chemical  indifference  is  shown  in  the  highest 
degree  by  nitrogen — an  element  which,  as  we  shall  hereafter 
see,  plays  the  leading  part  in  organic  changes. 

Among  the  organic  elements,  including  under  the  title 
not  only  the  four  chief  ones,  but  also  the  less  conspicuous  re- 
mainder, that  capability  of  assuming  different  states,  called 
allotropism,  is  frequent.  Carbon  presents  itself  in  the  three 
unlike  conditions  of  diamond,  graphite,  and  charcoal.  Under 
certain  circumstances,  oxygen  takes  on  the  form  in  which  it 
is  called  ozone.  Sulphur  and  phosphorus  (both,  in  small 
proportions,  essential  constituents  of  organic  matter)  have 
allotropic  modifications.  Silicon,  too,  is  allotropic ;  while 
its  oxide,  silica,  which  is  an  indispensable  constituent  of 
many  lower  organisms,  exhibits  the  analogue  of  allotropism 
— isomerism.  And  even  of  the  iron  which  plays  an  active 
part  in  higher  organisms,  and  a  passive  part  in  some  lower 
ones,  it  may  be  said  that  though  not  known  to  be  itself  allo- 
tropic, yet  isomerism  characterizes  those  compounds  of  it  that 
are  found  in  living  bodies.  Allotropism  being  interpretable 
as  some  change  of  molecular  arrangement,  this  frequency 
of  its  occurrence  among  the  components  of  organic  matter, 
is  significant  as  implying  a  further  kind  of  molecular  mobility. 


ORGANIC    MATTER.  5 

One  more  fact,  that  is  here  of  great  interest  for  ns,  must 
be  set  down.  These  four  elements  of  which  organisms  are 
almost  wholly  composed,  present  us  with  certain  extreme 
antitheses.  "While  between  two  of  them  we  have  an  unsur- 
passed contrast  in  chemical  activity  ;  between  one  of  them 
and  the  other  three,  we  have  an  unsurpassed  contrast  in 
molecular  mobility.  "While  carbon,  by  successfully  resisting 
fusion  and  volatilization  at  the  highest  temperatures  that  can 
be  produced,  shows  us  a  degree  of  atomic  cohesion  greater 
than  that  of  any  other  known  element,  hydrogen,  oxygen,  and 
nitrogen,  show  the  least  atomic  cohesion  of  all  elements.  And 
while  oxygen  displays,  alike  in  the  range  and  intensity  of  its 
affinities,  a  chemical  energy  exceeding  that  of  any  other  sub- 
stance (unless  fluorine  be  considered  an  exception),  nitrogen 
displays  the  greatest  chemical  inactivity.  Now  on  calling  to 
mind  one  of  the  general  truths  arrived  at  when  analyzing 
the  process  of  Evolution  the  probable  significance  of  this 
double  difference  will  be  seen.  It  was  shown  {First  Principles, 
§  123)  that,  other  things  equal,  unlike  units  are  more  easily 
separated  by  incident  forces  than  like  units'  are — that  an  inci- 
dent force  falling  on  units  that  are  but  little  dissimilar  does 
not  readily  segregate  them  ;  but  that  it  readily  segregates 
them  if  they  are  widely  dissimilar.  Thus,  these  two  extreme 
contrasts,  the  one  between  physical  mobilities,  and  the  other 
between  chemical  activities,  fulfil,  in  the  highest  degree,  a 
a  certain  further  condition  to  facility  of  differentiation  and 
integration. 

§  2.  Among  the  binary,  combinations  of  these  four  chief 
organic  elements,  we  find  a  molecular  mobility  much  less 
than  that  of  these  elements  themselves  ;  at  the  same  time 
that  it  is  much  greater  than  that  of  binary  compounds  in 
general.  Of  the  two  products  formed  by  the  union 

of  oxygen  with  carbon,  the  first,  called  carbonic  oxide,  which 
contains  one  atom  of  carbon  to  one  of  oxygen  (expressed  by 
the  symbol  C  O),  is  an  incondensible  gas ;  and  the  second 


THE    DATA    OF    BIOLOGY. 


carbonic  acid,  containing  an  additional  atom  of  oxygen  (C  02) 
assumes  a  liquid  form  only  under  a  pressure  of  nearly  forty 
atmospheres.  The  several  compounds  of  oxygen  with 

nitrogen,  present  us  with  an  instructive  gradation.  Protoxide 
of  nitrogen,  which  contains  one  atom  of  each  element  (N  O), 
is  a  gas  condensible  only  under  a  pressure  of  some  fifty  at- 
mospheres ;  deutoxide  of  nitrogen  (N  02)  is  a  gas  hitherto 
uncondensed  (the  molecular  mobility  remaining  undiminished 
in  consequence  of  the  volume  of  the  united  gases  remaining 
unchanged)  ;  nitrous  acid  (N  03)  is  gaseous  at  ordinary 
temperatures,  but  condenses  into  a  very  volatile  liquid  at  the 
zero  of  Fahrenheit ;  peroxide  of  nitrogen  (N  04)  is  gaseous  at 
71°,  liquid  between  that  and  16°,  and  becomes  solid  at  a  tem- 
perature below  this  ;  while  nitric  acid  (N  05)  may  be  obtained 
in  crystals  wmicli  melt  at  85°  and  boil  at  113°.  In  this 
series  we  see,  though  not  with  complete  uniformity,  a  de- 
crease of  molecular  mobility  as  the  weights  of  the  compound 
molecules   are  increased.  The   hydro-carbons   illus- 

trate the  same  general  truth  still  better.  One  series  of  them 
will  suffice.  Marsh  gas  (C2  H^  is  permanently  gaseous. 
Olefiant  gas  (C4  H4)  may  be  liquefied  by  pressure.  Oil 
gas,  which  is  identical  with  olefiant  gas  in  the  proportions 
of  its  constituents  but  has  double  the  atomic  weight,  (C8  H8\ 
becomes  liquid  without  pressure  at  the  zero  of  Fahrenheit. 
Amylene  (Ci0  Hio)  is  a  liquid  which  boils  to  102°.  And  the  suc- 
cessively higher  multiples,  caproylene  (C12  H12),  caprylene 
(C16  Hi6),  elaene  (C18  H18)  and  paramylene  (C^  H20),  are  liquids 
which  boil  respectively  at  102°,  131°,  257°,  230°,  and  329°. 
Cetylene  (C^  HS2)  is  a  liquid  which  boils  at  527°  ;  while  pa- 
raffine  (C54  H54)  and  mylene  (C60  H60)  are  solids.  Only 

one  compound  of  hydrogen  with  nitrogen  has  been  obtained 
in  a  free  state — ammonia  (H3  N)  ;  and  this,  which  is  gaseous, 
is  liquefiable  by  pressure,  or  by  reducing  its  temperature  to 
—  40°  F.  In  cyanogen,  which  is  composed  of  nitro- 

gen and  carbon  (N  C2),  we  have  a  gas  that  becomes  liquid  at  a 
pressure  of  four  atmospheres  and  solid  at  —  30°  F.     And,  in 


ORGANIC    MATTER.  / 

paracyanogen,  formed  of  the  same  proportions  of  these  ele- 
ments in  higher  multiples  (N3  C8),  we  have  a  solid  which  does 
not  fuse  or  volatilize  at  ordinary  temperatures.  Lastly, 

in  the  most  important  member  of  this  group,  water,  (H  O 
or  else  as  many  chemists  now  think  H2  02)  we  have  a  com- 
pound of  two  incondensible  gases  which  assumes  both  the 
fluid  state  and  the  solid  state  within  ordinary  ranges  of 
temperature ;  while  its  molecular  mobility  is  still  such  that 
its  fluid  or  solid  masses  are  continually  passing  into  the  form 
of  vapour,  though  not  with  great  rapidity  until  the  temper- 
ature is  raised  to  212°.* 

Considering  them  chemically,  it  is  to  be  remarked  of 
these  binary  compounds  of  the  four  chief  organic  elements, 
that  they  are,  on  the  average,  less  stable  than  binary  com- 
pounds in  general.  Water,  carbonic  oxide,  and  carbonic 
acid,  are,  it  is  true,  difficult  to  decompose.  But  omitting 
these,  the  usual  strength  of  union  among  the  elements  of  the 
above-named  substances  is    low  considering   the   simplicity 

*  This  immense  loss  of  molecular  mobility  which  oxygen  and  hydrogen  un- 
dergo on  uniting  to  form  water — a  loss  far  greater  than  that  seen  in  other  binary 
compounds  of  analogous  composition — suggests  the  conclusion  that  the  atom  of 
water  is  a  multiple  atom.  Thinking  that  if  this  conclusion  be  true,  some  evidence 
of  the  fact  must  be  afforded  by  the  heat-absorbing  power  of  aqueous  vapour, 
I  lately  put  the  question  to  Prof.  Tyndall,  whether  it  resulted  from  his  ex- 
periments that  the  vapour  of  water  absorbs  more  heat  than  the  supposed  sim- 
plicity of  its  atom  would  lead  him  to  expect.  I  learned  from  him  that  it  has  an 
excessive  absorbent  power — an  absorbent  power  more  like  that  of  the  complex- 
atomcd  vapours  than  like  that  of  the  simple-atomed  vapours — an  absorbent 
power  that  therefore  harmonizes  with  the  supposition  that  its  atom  is  a  multiple 
one.  Besides  this  anomalous  loss  of  molecular  mobility  and  this  anomalous  heat- 
absorbing  power,  there  are  other  facts  which  countenance  the  supposition.  The 
unparalleled  evolution  of  heat  during  the  combination  of  oxygen  and  hydrogen  is 
one.  Another  is  that  exceptional  property  which  water  possesses,  of  beginning  to 
expand  when  its  temperature  is  lowered  below  40° ;  since  this  exceptional  property 
is  explicable  only  on  the  assumption  of  some  change  of  molecular  arrangement — a 
change  which  is  comprehensible  if  the  molecules  are  multiple  ones.  And  yet  a 
further  confirmatory  fact  is  the  ability  of  water  to  assume  a  colloid  condition ;  for 
as  this  implies  a  capacity  in  its  atoms  for  aggregating  into  high  multiples,  it 
suggests,  by  analogy  with  known  cases,  that  they  have  a  capacity  for  aggregating 
into  lower  multiples. 


8  THE    DATA    OF   BIOLOGY. 

of  the  substances.  With  the  exception  of  acetylene,  the 
various  hydro-carbons  are  not  producible  by  directly  com- 
bining their  elements ;  and  the  elements  of  most  of  them  are 
readily  separated  by  heat  without  the  aid  of  any  antagonistic 
affinity.  Nitrogen  and  hydrogen  do  not  unite  with  each 
other  immediately ;  and  the  ammonia  which  results  from 
their  mediate  union,  though  it  resists  heat,  yields  to  the 
electric  spark.  Cyanogen  is  stable  :  not  being  resolved  into 
its  components  at  a  red  heat,  unless  in  iron  vessels.  Much 
less  stable  however  are  the  several  oxides  of  nitrogen.  The 
protoxide,  it  is  true,  does  not  yield  up  its  elements  below  a 
red  heat ;  but  nitrous  acid  cannot  exist  if  water  be  added  to 
it;  hypo-nitric  acid  is  decomposed  both  by  water. and  by 
contact  with  the  various  bases ;  and  nitric  acid  not  only 
readily  parts  with  its  oxygen  to  many  metals,  but  when 
anhydrous,  spontaneously  decomposes.  Here  it  will 

be  well  to  note,  as  having  a  bearing  on  what  is  to  follow,  how 
characteristic  of  most  nitrogenous  compounds  is  this  special 
instability.  In  all  the  familiar  cases  of  sudden  and  violent 
decomposition,  the  change  is  due  to  the  presence  of  nitrogen. 
The  explosion  of  gunpowder  results  from  the  readiness  with 
which  the  nitrogen  contained  in  the  nitrate  of  potash,  yields 
up  the  oxygen  combined  with  it.  The  explosion  of  gun-cot- 
ton, which  also  contains  nitric  acid,  is  a  substantially  par- 
allel phenomenon.  The  various  fulminating  salts  are  all 
formed  by  the  union  with  metals,  of  a  certain  nitrogenous 
acid  called  fulminic  acid  ;  which  is  so  unstable  that  it  cannot 
be  obtained  in  a  separate  state.  Explosiveness  is  a  property 
of  nitro-mannite,  and  also  of  nitro-glycerin.  Iodide  of  nitrogen 
detonates  on  the  slightest  touch,  and  often  without  any  assign- 
able cause.  Percussion  produces  detonation  in  sulphide  of 
nitrogen.  And  the  body  which  explodes  with  the  most 
tremendous  violence  of  any  that  is  known,  is  the  chloride  of 
nitrogen.  Thus  these  easy  and  rapid  decompositions,  due  to 
the  chemical  indiiference  of  nitrogen,  are  characteristic. 
When  we  come  hereafter  to  observe  the  part  which  nitrogen 


ORGANIC    MATTER.  9 

plays  in  organic  actions,  we  shall  see  the  significance  of  this 
extreme  readiness  shown  by  its  compounds  to  undergo 
change.  Returning  from  these  facts  parenthetically 

introduced,  we  have  next  to  note  that  though  among  these 
binary  compounds  of  the  four  chief  organic  elements,  there 
are  a  few  active  ones,  yet  the  majority  of  them  display  a 
smaller  degree  of  ehemical  energy  than  the  average  of  binary 
compounds.  Water  is  the  most  neutral  of  bodies  :  usually  pro- 
ducing little  chemical  alteration  in  the  substances  with  which 
it  combines ;  and  being  expelled  from  most  of  its  combinations 
by  a  moderate  heat.  Carbonic  acid  is  a  relatively  feeble  acid  : 
the  carbonates  being  decomposed  by  the  majority  of  other  acids 
and  by  ignition.  The  various  hydro-carbons  are  but  narrow 
in  the  range  of  their  comparatively  weak  affinities.  The 
compounds  formed  by  ammonia  have  not  much  stability  :  they 
are  readily  destroyed  by  heat,  and  by  the  other  alkalies. 
The  affinities  of  cyanogen  are  tolerably  strong ;  though  they 
yield  to  those  of  the  chief  acids.  Of  the  several  oxides  of  ni- 
trogen it  is  to  be  remarked,  that  while  those  containing  the 
smaller  proportions  of  oxygen  are  chemically  inert,  that  con- 
taining the  greatest  proportion  of  oxygen  (nitric  acid)  though 
chemically  active,  in  consequence  of  the  readiness  with  which 
one  part  of  it  gives  up  its  oxygen  to  oxidize  a  base  with 
which  the  rest  combines,  is  nevertheless  driven  from  all  its 
combinations  by  a  red  heat. 

These  binary  compounds,  like  their  elements,  are  to  a  con- 
siderable degree  characterized  by  the  prevalence  among 
them  of  allotropism  ;  or,  as  it  is  more  usually  called  when 
displayed  by  compound  bodies — isomerism.  Professor  Graham 
finds  reason  for  thinking  that  a  change  in  atomic  arrange- 
ment of  this  nature,  takes  place  in  water,  at  or  near  the 
melting  point  of  ice.  The  relation  between  cyanogen  and 
paracyanogen  is,  as  we  saw,  an  isomeric  one.  In  the  above- 
named  series  of  hydro-carbons,  differing  from  each  other  only 
in  the  multiples  in  which  the  elements  are  united,  we  find 
isomerism  becoming  what  is  distinguished   as  polymerism. 


10  THE   DATA    OF    BIOLOGY. 

The  like  is  still  more  conspicuous  in  other  groups  of  the 
hydro-carbons,  as  in  the  essential  oils :  sixteen  to  twenty  of 
which  are  severally  isomeric  with  essential  oil  of  turpentine. 
Here  the  particular  kind  of  molecular  mobility  implied  by 
these  metamorphoses,  is  well  shown :  essential  oil  of  turpen- 
tine being  converted  into  a  mixture  of  several  of  these  poly- 
merides,  by  simple  exposure  to  a  heat  of  460°. 

There  is  one  further  fact  respecting  these  binary  compounds 
of  the  four  chief  organic  elements,  which  must  not  be  over- 
looked. Those  of  them  which  form  parts  of  the  living  tissues 
of  plants  and  animals  (excluding  water  which  has  a  me- 
chanical function,  and  carbonic  acid  which  is  a  product  of 
decomposition)  are  confined  to  one  group — the  hydro-carbons. 
And  of  this  group,  which  is  on  the  average  characterized  by 
comparative  instability  and  inertness,  these  hydro-carbons 
found  in  living  tissues,  are  among  the  most  unstable  and 
inert. 

§  3.  Passing  now  to  the  substances  which  contain  three 
of  these  chief  organic  elements,  we  have  first  to  note  that 
along  with  the  greater  atomic  weight  which  mostly  accom- 
panies their  increased  complexity,  there  is,  on  the  average, 
a  further  marked  decrease  of  molecular  mobility.  Scarcely  any 
of  them  maintain  a  gaseous  state  of  ordinary  temperatures. 
One  class  of  them  only,  the  alcohols  and  their  derivatives, 
evaporate  under  the  usual  atmospheric  pressure ;  but  not 
rapidly  unless  heated.  The  fixed  oils,  though  they  show  that 
molecular  mobility  implied  by  an  habitually  liquid  state, 
show  this  in  a  lower  degree  than  the  alcoholic  compounds ; 
and  they  cannot  be  reduced  to  the  gaseous  state  without  de- 
composition. In  their  allies,  the  fats,  which  are  solid  unless 
heated,  the  loss  of  molecular  mobility  is  still  more  marked. 
And  throughout  the  whole  series  of  the  fatty  acids,  in  which 
to  a  fixed  proportion  of  oxygen  there  are  successively  added 
higher  equimultiples  of  carbon  and  hydrogen,  we  see  how 
the  molecular  mobility  decreases  with  the  increasing  sizes  of 


ORGANIC    MATTER.  11 

the  atoms.  In  the  amylaceous  and  saccharine  group  of  com- 
pounds, solidity  is  the  habitual  state :  such  of  them  as  can 
assume  a  liquid  form,  doing  so  only  when  heated  to  300°  or 
400°  F. ;  and  decomposing  when  further  heated,  rather  than 
become  gaseous.  Resins  and  gums  exhibit  general  physical 
properties  of  like  character  and  meaning. 

In  chemical  stability  these  ternary  compounds,  considered 
as  a  group,  are  in  a  marked  degree  below  the  binary  ones. 
The  various  sugars  and  kindred  bodies,  decompose  at  no  very 
high  temperatures.  The  oils  and  fats  are  also  readily  carbon- 
ized by  heat.  Resinous  and  gummy  substances  are  easily 
made  to  render  up  some  of  their  constituents.  And  the 
alcohols  with  their  allies,  have  no  great  power  of  resisting 
decomposition.  These  bodies,  formed  by  the  union  of 

oxygen,  lrydrogen,  and  carbon,  are  also,  as  a  class,  chemically 
inactive.  The  formic  and  acetic  are  doubtless  energetic 
acids ;  but  the  higher  members  of  the  fatty-acid  series  are 
easily  separated  from  the  bases  with  which  they  combine. 
Saccharic  acid,  too,  is  an  acid  of  considerable  power ;  and 
sundry  of  the  vegetal  acids  possess  a  certain  activity, 
though  an  activity  far  less  than  that  of  the  mineral  acids. 
But  throughout  the  rest  of  the  group,  there  is  shown  but  a 
small  tendency  to  combine  with  other  bodies  ;  and  such  com- 
binations as  are  formed  have  usually  little  permanence. 

The  phenomena  of  isomerism  and  polymerism  are  of  fre- 
quent occurrence  in  these  ternary  compounds.  Starch  and 
dextrine  are  isomeric.  Fruit  sugar,  starch  sugar,  eucalvn, 
sorbin,  and  inosite,  are  polymeric.  Sundry  of  the  vegetal 
acids  exhibit  similar  modifications.  And  among  the  resins 
and  gums,  with  their  derivatives,  molecular  re-arrangements 
of  this  kind  are  not  uncommon. 

One  further  fact  respecting  these  compounds  of  carbon, 
oxygen  and  hydrogen,  should  be  mentioned ;  namely,  that 
they  are  divisible  into  two  classes — the  one  consisting  of  sub- 
stances that  result  from  the  destructive  decomposition  of 
organic  matter,  and  the  other  consisting  of  substances  that 


12  THE    DATA   OF    BIOLOGY. 

exist  as  such  in  organic  matter.  These  two  classes  of  sub- 
stances exhibit  in  different  degrees,  the  properties  to  which 
we  have  been  directing  our  attention.  The  lower  alcohols, 
their  allies  and  derivatives,  which  possess  greater  molecular 
mobility  and  chemical  stability  than  the  rest  of  these  ternary 
compounds,  are  not  found  in  animal  or  vegetal  bodies.  While 
the  sugars  and  amylaceous  substances,  the  fixed  oils  and  fats, 
the  gums  and  resins,  which  have  all  of  them  much  less  mole- 
cular mobility,  and  are,  chemically  considered,  more  unstable 
and  inert,  are  components  of  the  living  tissues  of  plants  and 
animals. 

§  4.  Among  compounds  containing  all  the  four  chief 
organic  elements,  a  division  analogous  to  that  just  named 
may  be  made.  There  are  some  which  result  from  the  decom- 
position of  living  tissues ;  there  are  others  which  make 
parts  of  living  tissues  in  their  state  of  integrity ;  and  these 
two  groups  are  contrasted  in  their  properties  in  the  same  way 
as  are  the  parallel  groups  of  ternary  compounds. 

Of  the  first  division,  certain  products  found  in  the  animal 
excretions  are  the  most  important,  and  the  only  ones  that 
need  be  noted  ;  such,  namely,  as  urea,  kreatine,  kreatinine. 
These  animal  bases  exhibit  much  less  molecular  mobility  than 
the  average  of  the  substances  treated  of  in  the  last  section  : 
being  solid  at  ordinary  temperatures,  fusing,  where  fusible  at 
all,  at  temperatures  above  that  of  boiling  water,  and  having 
no  power  to  assume  a  gaseous  state.  Chemically  considered, 
their  stability  is  low,  and  their  activity  but  small,  in  com- 
parison with  the  stabilities  and  activities  of  the  simpler  com- 
pounds. 

It  is,  however,  the  nitrogenous  constituents  of  living  tis- 
sues, that  display  most  markedly,  those  characteristics  of  which 
we  have  been  tracing  the  growth.  Albumen,  fibrin,  casein, 
and  their  allies,  are  bodies  in  which  that  molecular  mobility 
exhibited  by  three  of  their  components  in  so  high  a  degree, 
is  reduced  to  a  minimum.     These  substances  are  known  only 


ORGANIC    MATTER.  13 

in  the  solid  state :  that  is  to  say,  when  deprived  of  the  water 
usually  mixed  with  them,  they  do  not  admit  of  fusion,  much 
less  of  volatilization.  To  which  add,  that  they  have  not  even 
that  molecular  mobility  which  solution  in  water  implies; 
since  though  the}'  form  viscid  mixtures  with  water,  they  do 
not  dissolve  in  the  same  perfect  way  as  do  inorganic  com- 
pounds. The  chemical  characteristics  of  these  sub- 
stances, are  instability  and  inertness  carried  to  the  extreme. 
How  rapidly  albumenoid  matters  decompose  under  ordinary 
conditions,  is  daily  seen :  the  difficulty  of  every  house-wife 
being  to  prevent  them  from  decomposing.  It  is  true  that 
when  desiccated  and  kept  from  contact  with  air,  they  may  be 
preserved  unchanged  for  a  long  period  ;  but  the  fact  that  they 
can  only  be  thus  preserved,  proves  their  great  instability.  It  is 
true,  also,  that  these  most  complex  nitrogenous  principles  are 
not  absolutely  inert;  since  they  enter  into  combinations  with 
some  bases ;  but  their  unions  are  very  feeble. 

It  should  be  noted,  too,  of  these  bodies,  that  though  they 
exhibit  in  the  lowest  degree  that  kind  of  molecular  mobility, 
which  implies  facile  vibration  of  the  atoms  as  wholes,  they  ex- 
hibit in  a  high  degree  that  kind  of  molecular  mobility  resulting 
in  isomerism,  which  implies  permanent  changes  in  the  posi- 
tions of  adjacent  atoms  with  respect  to  each  other.  Each  of 
them  has  a  soluble  and  insoluble  form.  In  some  cases  there 
are  indications  of  more  than  two  such  forms.  And  it  appears 
that  their  metamorphoses  take  place  under  very  slight 
changes  of  conditions. 

In  these  most  unstable  and  inert  organic  compounds,  we 
find  that  the  atomic  complexity  reaches  a  maximum :  not 
only  since  the  four  chief  organic  elements  are  here  united 
with  small  proportions  of  sulphur  and  phosphorus;  but  also 
since  they  are  united  in  high  multiples.  The  peculiarity 
which  we  found  characterized  even  binary  compounds  of  the 
organic  elements,  that  their  atoms  are  formed  not  of  single 
equivalents  of  each  component,  but  of  two,  three,  four  and 
more  equivalents,  is  carried  to  the  greatest  extreme  in  these 


14  THE    DATA    OF    BIOLOGY. 

compounds,  that  take  the  leading  part  in  organic  actions. 
According  to  Mulder,  the  formula  of  albumen  is  10  (C40  H81 
R5  qi2j  _|_  g2  p  That  is  to  sa}7,  with  the  sulphur  and  phos- 
phorus there  are  united  ten  equivalents  of  a  compound  atom 
containing  forty  atoms  of  carbon,  thirty-one  of  hydrogen, 
live  of  nitrogen,  and  twelve  of  oxygen  :  the  atom  being  thus 
made  up  of  nearly  nine  hundred  ultimate  atoms. 

§  5.  Did  space  permit,  it  would  be  useful  here  to  consider 
in  detail,  the  interpretations  that  may  be  given  of  the  pecu- 
liarities we  have  been  tracing :  bringing  to  their  solution, 
those  general  mechanical  principles  which  are  now  found  to 
hold  true  of  molecules  as  of  masses.  But  it  must  suffice 
briefly  to  indicate  the  conclusions  that  such  an  inquiry  pro- 
mises to  bring  out. 

Proceeding  on  mechanical  principles,  it  may  be  argued  that 
the  molecular  mobility  of  a  substance  must  depend  partly  on 
the  inertia  of  its  molecules;  partly  on  the  intensity  of  their 
mutual  polarities;  partly  on  their  mutual  pressure,  as  deter- 
mined by  the  density  of  their  aggregation,  and  (where  the 
molecules  are  compound)  partly  on  the  molecular  mobilities 
of  their  component  molecules.  Whence  it  is  to  be  inferred 
that  any  three  of  these  remaining  constant,  the  molecular 
mobility  will  vary  as  the  fourth.  Other  things  equal,  there- 
fore, the  molecular  mobility  of  atoms  must  decrease  as  their 
masses  increase ;  and  so  there  must  result  that  general  pro- 
gression we  have  traced,  from  the  high  molecular  mobility 
of  the  uncombined  organic  elements,  to  the  low  molecular 
mobility  of  those  large-atomed  substances  into  which  they  are 
ultimately  compounded. 

Applying  to  atoms  the  mechanical  law  which  holds  of 
masses,  that  since  inertia  and  gravity  increase  as  the  cubes 
of  the  dimensions  while  cohesion  increases  as  their  squares, 
the  self-sustaining  power  of  a  body  becomes  relatively 
smaller  as  its  bulk  becomes  greater ;  it  might  be  argued  that 
these  large,  aggregate  atoms  which  constitute  organic  sub- 


ORGANIC    MATTER.  15 

stance,  arc  mechanically  weak — are  less  able  than  simpler 
atoms  to  bear,  without  alteration,  the  forces  falling  on  them. 
That  very  massiveness  which  renders  them  less  mobile,  enables 
the  physical  forces  acting  on  them  more  readily  to  change  the 
relative  positions  of  their  component  atoms  ;  and  so  to  pro- 
duce what  we  know  as  re-arrangements  and  decompositions. 
Further,  it  seems  a  not  improbable  conclusion,  that  this 
formation  of  large  aggregates  of  elementary  atoms,  and  re- 
sulting diminution  of  self-sustaining  power,  must  be  accom- 
panied by  a  decrease  of  those  contrasts  of  dimension  to 
which  polarity  is  ascribable.  A  sphere  is  the  figure  of  equi- 
librium which  any  aggregate  of  units  tends  to  assume,  under 
the  influence  of  simple  mutual  attraction.  AVhere  the  num- 
ber of  units  is  small  and  their  mutual  polarities  are  decided, 
this  proclivity  towards  spherical  grouping  will  be  overcome 
by  the  tendency  towards  some  more  special  form,  determined 
by  their  mutual  polarities.  But  it  is  manifest  that  in  pro- 
portion as  an  aggregate  atom  becomes  larger,  the  effects  of 
simple  mutual  attraction  must  become  relatively  greater ; 
and  so  must  tend  to  mask  the  effects  of  polar  attraction. 
There  will  consequently  be  apt  to  result  in  highly  com- 
pound atoms  like  these  organic  ones  containing  nine  hun- 
dred elementary  atoms,  such  approximation  to  the  spherical 
form  as  must  involve  a  less  distinct  polarit}T  than  in  simpler 
atoms.  If  this  inference  be  correct,  it  supplies  us  with  an  ex- 
planation both  of  the  chemical  inertness  of  these  most  com- 
plex organic  substances,  and  of  their  inability  to  crystallize. 

j;  6.  Here  we  are  naturally  introduced  to  another  aspect  of 
our  subject — an  aspect  of  great  interest.  Professor  Graham 
has  recently  published  a  series  of  important  researches,  which 
promise  to  throw  much  light  on  the  constitution  and  changes 
of  organic  matter.  He  shows  that  solid  substances  exist  un- 
der two  forms  of  aggregation — the  colloid  or  jelly-like,  and  the 
crystalloid  or  crystal-like.  Examples  of  the  last  are  too  fa- 
miliar to  need  specifying.     Of  the  first  may  be  named  such 


16  THE   DATA    OF   BIOLOGY. 

instances  as  "  hydrated  silicic  acid,  hydrated  alumina,  and 
other  metallic  peroxides  of  the  aluminous  class,  when  they  exist 
in  the  soluble  form  ;  with  starch,  dextrine  and  the  gums,  cara- 
mel, tannin,  albumen,  gelatine,  vegetable  and  animal  extractive 
matters."  Describing  the  properties  of  colloids,  Professor 
Graham  says  : — "  Although  often  largely  soluble  in  water, 
they  are  held  in  solution  by  a  most  feeble  force.  They  ap- 
pear singularly  inert  in  the  capacity  of  acids  and  bases,  and 
in  all  the  ordinary  chemical  relations."  *  *  *  "Al- 
though chemically  inert  in  the  ordinary  sense,  colloids 
possess  a  compensating  activity  of  their  own  arising  out  of 
their  physical  properties.  "While  the  rigidity  of  the  crystal- 
line structure  shuts  out  external  impressions,  the  softness  of 
the  gelatinous  colloid  partakes  of  fluidity,  and  enables  the 
colloid  to  become  a  medium  of  liquid  diffusion,  like  water 
itself."  *  *  *  "  Hence  a  wide  sensibility  on  the  part  of 
colloids  to  external  agents.  Another  and  eminently  charac- 
teristic quality  of  colloids  is  their  mutability."  *  *  *  "  The 
solution  of  hydrated  silicic  acid,  for  instance,  is  easily  obtain- 
ed in  a  state  of  purity,  but  it  cannot  be  preserved.  It  may 
remain  fluid  for  days  or  weeks  in  a  sealed  tube,  but  is  sure  to 
gelatinize  and  become  insoluble  at  last.  Nor  does  the  change 
of  this  colloid  appear  to  stop  at  that  point ;  for  the  mineral 
forms  of  silicic  acid,  deposited  from  water,  such  as  flint,  are 
often  found  to  have  passed,  during  the  geological  ages  of 
their  existence,  from  the  vitreous  or  colloidal  into  the  crystal- 
line condition  (H.  Rose).  The  colloid  is,  in  fact,. a  dynami- 
cal state  of  matter,  the  crystalloidal  being  the  statical 
condition.  The  colloid  possesses  energia.  It  may  be  looked 
upon  as  the  primary  source  of  the  force  appearing  in  the 
phenomena  of  vitality.  To  the  gradual  manner  in  which 
colloidal  changes  take  place  (for  they  always  demand  time  as 
an  element)  may  the  characteristic  protraction  of  chemico- 
organic  changes  also  be  referred." 

The  class  of  colloids  includes  not  only  all  those  most  com- 
plex nitrogeneous  compounds  characteristic  of  organic  tissue^ 


ORGANIC    MATTER.  17 

and  sundry  of  the  oxy-hvdro-carbons  found  along  with  them  ; 
but,  significantly  enough,  it  includes  several  of  those  sub- 
stances classed  as  inorganic,  which  enter  into  organized 
structures.  Thus  silica,  which  is  a  component  of  many 
plants,  and  constitutes  the  spicules  of  sponges  as  well  as  the 
shells  of  many  foraminifera  and  infusoria,  has  a  colloid,  as 
well  as  a  crystalloid,  condition.  A  solution  of  hyd rated  silicic 
acid,  passes  in  the  course  of  a  few  days  into  a  solid  jelly  that 
is  no  longer  soluble  in  water  ;  and  it  may  be  suddenly  thus 
coagulated  by  a  minute  portion  of  an  alkaline  carbonate,  as 
well  as  by  gelatine,  alumina,  and  peroxide  of  iron.  This  last- 
named  substance,  too — peroxide  of  iron — which  is  an  ingre- 
dient in  the  blood  of  mammals  and  composes  the  shells  of 
certain  protozoa,  has  a  colloid  condition.  "  Water  containing 
about  one  per  cent,  of  hydrated  peroxide  of  iron  in  solution, 
has  the  dark  red  colour  of  venous  blood."  *  *  *  "  The 
red  solution  is  coagulated  in  the  cold  by  traces  of  sulphuric 
acid,  alkalies,  alkaline  carbonates,  sulphates,  and  neutral  salts 
in  general."  *  *  *  "  The  coagulum  is  a  deep  red-coloured 
jelly,  resembling  the  clot  of  blood  but  more  transparent. 
Indeed,  the  coagulum  of  this  colloid  is  highly  suggestive 
of  that  of  blood,  from  the  feeble  agencies  which  suffice  to 
effect  the  change  in  question,  as  well  as  from  the  appearance 
of  the  product."  The  jelly  thus  formed  soon  becomes,  like 
the  last,  insoluble  in  water.  Lime  also,  which  is  so  important 
a  mineral  element  in  living  bodies,  animal  and  vegetal 
enters  into  a  compound  belonging  to  this  class.  "  The 
well-known  solution  of  lime  in  sugar,  forms  a  solid  coagulum 
when  heated.  It  is  probably,  at  a  high  temperature,  entirely 
colloidal." 

Generalizing  some  of  the  facts  which  he  gives,  Professor 
Graham  says — "The  equivalent  of  a  colloid  appears  to  be 
always  high,  although  the  ratio  between  the  elements  of  the 
substance  may  be  simple.  Gummic  acid,  for  instance,  may 
be  represented  by  C12  Hu  O1  ;  but,  judging  from  the  small 
proportions  of  lime  and  potash  which  suffice  to  neutralize  this 


18  THE    DATA    OF    BIOLOGY. 

acid,  the  true  numbers  of  its  formula  must  be  several  times 
greater.  It  is  difficult  to  avoid  associating  the  inertness  of 
colloids  with  their  high  equivalents,  particularly  where  the 
high  number  appears  to  be  attained  by  the  repetition  of  a 
small  number.  The  inquiry  suggests  itself  whether  the  col- 
loid molecule  may  not  be  constituted  by  the  grouping 
together  of  a  number  of  smaller  crystalloid  molecules,  and 
whether  the  basis  of  colloidality  may  not  really  be  this  com- 
posite character  of  the  molecule." 

§  7.  A  further  contrast  between  colloids  and  crystalloids, 
is  equally  significant  in  its  relations  to  vital  phenomena. 
Professor  Graham  points  out  that  the  marked  differences  in 
volatility  displayed  by  different  bodies,  are  paralleled  by 
differences  in  the  rates  of  diffusion  of  different  bodies  through 
liquids.  As  alcohol  and  ether  at  ordinary  temperatures,  and 
various  other  substances  at  higher  temperatures,  diffuse  them- 
selves in  a  gaseous  form  through  the  air;  so  a  substance  in 
aqueous  solution,  when  placed  in  contact  with  a  mass  of 
water  (in  such  way  as  to  avoid  mixture  by  circulating  currents) 
diffuses  itself  through  this  mass  of  water.  And  just  as  there 
are  various  degrees  of  rapidity  in  evaporation,  so  there  are 
various  degrees  of  rapidity  in  diffusion  :  "  the  range  also  in 
the  degree  of  diffusive  mobility  exhibited  by  different  sub- 
stances appears  to  be  as  wide  as  the  scale  of  vapour-tensions." 
This  parallelism  is  what  might  have  been  looked  for  ;  since 
the  tendency  to  assume  a  gaseous  state,  and  the  tendency  to 
spread  in  solution  through  a  liquid,  are  both  consequences  of 
molecular  mobility.  It  also  turns  out,  as  was  to  be  expected, 
that  diffusibility,  like  volatility,  has,  other  things  equal,  a  re- 
lation to  atomic  weight — (other  things  equal,  we  must  say, 
because  molecular  mobility  must,  as  pointed  out  in  §  5,  be 
affected  by  other  properties  of  atoms,  besides  their  inertia). 
Thus  the  substance  most  rapidly  diffused  of  any  on  which 
Professor  Graham  experimented,  was  hydro-chloric  acid — a 
compound  which  is  of  low  atomic  weight,  is  gaseous  save 


ORGANIC   MATTER.  19 

under  a  pressure  of  forty  atmospheres,  and  ordinarily  exists 
as  a  liquid,  only  in  combination  with  water.  Again,  "  hydrate 
of  potash  may  be  said  to  possess  double  the  velocity  of  diffu- 
sion of  sulphate  of  potash,  and  sulphate  of  potash  again  double 
the  velocity  of  sugar,  alcohol,  and  sulphate  of  magnesia," — 
differences  which  have  a  general  correspondence  with  differ- 
ences in  the  massiveness  of  the  atoms. 

But  the  fact  of  chief  interest  to  us  here,  is  that  the  rela- 
tively small -atomed  crystalloids  have  immensely  greater 
diffusive  power  than  the  relatively  large -atomed  colloids. 
Among  the  crystalloids  themselves,  there  are  marked  differ- 
ences of  diffusibility  ;  and  among  the  colloids  themselves, 
there  are  parallel  differences,  though  less  marked  ones.  But 
these  differences  are  small  compared  with  that  between  the 
diffusibility  of  the  crystalloids  as  a  class,  and  the  diffusibility 
of  the  colloids  as  a  class.  Hydro-chloric  acid  is  seven  times 
as  diffusible  as  sulphate  of  magnesia ;  but  it  is  fifty  times 
as  diffusible  as  albumen,  and  a  hundred  times  as  diffusible 
as  caramel. 

These  differences  of  diffusibility  manifest  themselves  with 
nearly  equal  distinctness,  when  a  permeable  septum  is  placed 
between  the  solution  and  the  water.  And  the  result  is,  that 
when  a  solution  contains  substances  of  different  diffusibilities, 
the  process  of  dialysis,  as  Professor  Graham  calls  it,  becomes 
a  means  of  separating  the  mixed  substances  :  especially  when 
such  mixed  substances  are  partly  crystalloids  and  partly  col- 
loids. The  bearing  of  this  fact  on  organic  processes  will  be 
obvious.  Still  more  obvious  will  its  bearing  be,  on 

joining  it  with  the  remarkable  fact,  that  while  crystalloids 
can  diffuse  themselves  through  colloids  nearly  as  rapidly  as 
through  water,  colloids  can  scarcely  diffuse  themselves  at  all 
through  other  colloids.  From  a  mass  of  jelly  containing 
salt,  into  an  adjoining  mass  of  jelly  containing  no  salt,  the 
salt  spread  more  in  eight  days  than  it  spread  through  water 
in  seven  days;  while  the  spread  of  "caramel  through  the 
jelly  appeared  scarcely  to  have  begun  after  eight  days  had 


20  THE    DATA    OF    BIOLOGY. 

elapsed."  So  that  we  must  regard  the  colloidal  compounds 
of  which  organisms  are  built,  as  having  by  their  physical 
nature,  the  ability  to  separate  colloids  from  crystalloids,  and 
to  let  the  crystalloids  pass  through  them  with  scarcely  any 
resistance. 

One  other  result  of  these  researches  on  the  relative  diffu- 
sibilities  of  different  substances,  has  a  meaning  for  us.  Pro- 
fessor Graham  rinds,  that  not  only  does  there  take  place  by 
dialysis,  a  separation  of  mixed  substances  which  are  unlike  in 
their  molecular  mobilities  ;  but  also  that  combined  substances 
between  which  the  affinity  is  feeble,  will  separate  on  the 
dialyzer,  if  their  molecular  mobilities  are  strongly  -con- 
trasted. Speaking  of  the  hydro-chlorate  of  peroxide  of 
iron,  he  says,  "  such  a  compound  possesses  an  element  of 
instability  in  the  extremely  unequal  diffusibility  of  its 
constituents  ; "  and  he  points  out  that  when  dialyzed,  the 
hydro-chloric  acid  gradually  diffuses  away,  leaving  the 
colloidal  peroxide  of  iron  behind.  Similarly,  he  remarks  of 
the  peracetate  of  iron,  that  it  "  may  be  made  a  source  of 
soluble  peroxide,  as  the  salt  referred  to  is  itself  decomposed 
to  a  great  extent  by  diffusion  on  the  dial}7zer."  Now  this 
tendency  to  separate  displayed  by  substances  that  differ 
widely  in  their  molecular  mobilities,  though  usually  so 
far  antagonized  by  their  affinities  as  not  to  produce  sponta- 
neous decomposition,  must,  in  all  cases,  induce  a  certain 
readiness  to  change  which  would  not  else  exist.  The  un- 
equal mobilities  of  the  combined  atoms,  must  give  disturbing 
forces  a  greater  power  to  work  transformations  than  they 
would  otherwise  have.  Hence  the  probable  significance  of  a 
fact  named  at  the  outset,  that  while  three  of  the  chief  organic 
elements  have  the  greatest  atomic  mobilities  of  any  elements 
known,  the  fourth,  carbon,  has  the  least  atomic  mobility  of 
known  elements.  Though,  in  its  simple  compounds,  the 
affinities  of  carbon  for  the  rest  are  strong  enough  to  prevent 
the  effects  of  this  great  difference  from  clearly  showing  them- 
selves ;  yet  there  seems  reason  to  think,  that  in  those  com- 


ORGANIC    MATTER.  21 

plex  compounds  composing  organic  bodies — compounds  in 
which  there  are  various  cross  affinities  leading  to  a  state 
of  chemical  tension — this  extreme  difference  in  the  molecular 
mobilities  must  be  an  important  aid  to  molecular  re-arrange- 
ments. In  short,  we  are  here  led  by  concrete  evidence  to  the 
conclusion  which  we  before  drew  from  first  principles,  that 
this  great  unlikeness  among  the  combined  units  must  facili- 
tate differentiations. 

§  8.  A  portion  of  organic  matter  in  a  state  to  exhibit  those 
phenomena  which  the  biologist  deals  with,  is,  however,  some- 
thing far  more  complex  than  the  separate  organic  matters 
we  have  been  studying ;  since  a  portion  of  organic  matter  in 
its  integrity,  contains  several  of  these. 

In  the  first  place,  no  one  of  those  colloids  which  make  up 
the  mass  of  a  living  body,  appears  capable  of  carrying  on 
vital  changes  by  itself  :  it  is  always  associated  with  other 
colloids.  A  portion  of  animal-tissue,  however  minute,  almost 
always  contains  more  than  one  form  of  protein-substance : 
different  chemical  modifications  of  albumen  and  gelatine  are 
present  together,  as  well  as,  probably,  a  soluble  and  insoluble 
modification  of  each ;  and  there  is  usually  more  or  less  of 
fatty  matter.  In  a  single  vegetal  cell,  the  minute  quantity 
of  nitrogenous  colloid  present,  is  imbedded  in  colloids  of  the 
non-nitrogenous  class.  The  microscope  makes  it  at  once 
manifest,  that  even  the  smallest  and  simplest  organic  forms 
are  not  absolutely  homogeneous. 

Further,  we  have  to  contemplate  organic  tissue,  formed 
of  mingled  colloids  in  both  soluble  and  insoluble  states,  as 
permeated  throughout  by  crystalloids.  Some  of  these  crys- 
talloids, as  oxygen,*  water,  and  perhaps  certain  salts,  are 
agents  of  decomposition ;  some,  as  the  saccharine  and  fatty 

*  It  will  perhaps  seem  strange  to  class  oxygen  as  a  crystalloid.  But  inasmuch 
as  the  crystalloids  are  distinguished  from  the  colloids  by  their  atomic  simplicity, 
and  inasmuch  as  sundry  gases  are  reducible  to  a  crystalline  state,  we  are  justi- 
fied in  so  classing  it. 


22  THE    DATA    OF    BIOLOGY. 

matters,  are  probably  materials  for  decomposition  ;  and  some, 
as  carbonic  acid,  water,  urea,  kreatine,  and  kreatinine,  are 
products  of  decomposition.  Into  the  mass  of  mingled  colloids, 
mostly  insoluble  and  where  soluble  of  very  low  molecular 
mobility  or  diffusive  power,  we  have  constantly  passing,  crys- 
talloids of  high  molecular  mobility  or  diffusive  power,  that 
are  capable  of  decomposing  these  complex  colloids ;  and  from 
these  complex  colloids,  so  decomposed,  there  result  other 
crystalloids  (the  two  chief  ones  extremely  simple  and  mobile, 
and  the  rest  comparatively  so)  which  diffuse  away  as  rapidly 
as  they  are  formed. 

And  now  we  may  clearly  see  the  necessity  for  that  pecu- 
liar composition  which  we  find  in  organic  matter.  On  the 
one  hand,  were  it  not  for  the  extreme  molecular  mobility 
possessed  by  three  of  its  chief  elements  out  of  the  four ;  and 
were  it  not  for  the  consequently  high  molecular  mobility  of 
their  simpler  compounds  ;  there  could  not  be  this  quick  escape 
of  the  waste  products  of  organic  action  ;  and  there  could  not 
be  that  continuously  active  change  of  matter  which  vitality 
implies.  On  the  other  hand,  were  it  not  for  the  union  of 
these  extremely  mobile  elements  into  immensely  complex 
compounds,  having  relatively  vast  atoms  that  are  made  com- 
paratively immobile  by  their  inertia,  there  could  not  result 
that  mechanical  fixity  which  prevents  the  components  of  liv- 
ing tissue  from  diffusing  away  along  with  the  effete  matters 
produced  by  the  decomposition  of  tissue. 

§  9.  Thus  in  the  substances  of  which  organisms  are  com- 
posed, the  conditions  necessary  to  that  re-distribution  of 
Matter  and  Motion  which  constitutes  Evolution,  are  fulfilled 
in  a  far  higher  degree  than  at  first  appears. 

The  mutual  affinities  of  the  chief  organic  elements  are 
not  active  within  the  limits  of  those  temperatures  at  which 
organic  actions  take  place ;  and  one  of  these  elements  is 
especially  characterized  by  its  chemical  indifference.  The 
compounds  formed  by  these  elements  in  ascending  grades  of 


ORGANIC    MATTER.  23 

complexity,  become  progressively  less  stable.  And  those 
most  complex  compounds  into  which  all  these  four  elements 
enter,  together  with  small  proportions  of  two  other  elements 
that  very  readily  oxidize,  have  an  instability  so  great  that 
decomposition  ensues  under  ordinary  atmospheric  conditions. 

Among  these  elements  out  of  which  living  bodies  are  built, 
there  is  an  unusual  tendency  to  unite  in  multiples ;  and  so  to 
form  groups  of  products  which  have  the  same  chemical  com- 
ponents, but,  being  different  in  their  modes  of  aggregation, 
possess  different  properties.  This  prevalence  among  them  of 
isomerism  and  polymerism,  shows,  in  another  way,  the  special 
fitness  of  organic  substances  for  undergoing  re-distributions. 

In  those  most  complex  compounds  that  are  instrumental 
to  vital  actions,  there  exists  a  kind  and  degree  of  molecular 
mobility  which  constitutes  the  plastic  quality  fitting  them  for 
organization.  Instead  of  the  extreme  molecular  mobility 
possessed  by  three  out  of  the  four  organic  elements  in  their 
separate  states — instead  of  the  diminished,  but  still  great, 
molecular  mobility  possessed  by  their  simpler  combinations, 
the  gaseous  and  liquid  characters  of  which  unfit  them  for 
showing  to  any  extent  the  process  of  Evolution — instead  of 
the  properties  of  their  less  simple  combinations,  which, 
when  not  made  unduly  mobile  by  heat,  assume  the  unduly 
rigid  form  of  crystals  ;  we  have  in  these  colloids,  of  which 
organisms  are  mainly  composed,  just  the  required  com- 
promise between  fluidity  and  solidity.  They  cannot  be  re- 
duced to  the  unduly  mobile  conditions  of  liquid  and  gas  ;  and 
yet  they  do  not  assume  the  unduly  fixed  conditions  usually  cha- 
racterizing solids.  The  absence  of  power  to  unite  together  in 
polar  arrangement,  leaves  their  atoms  with  a  certain  freedom 
of  relative  movement  which  makes  them  sensitive  to  small 
forces,  and  produces  plasticity  in  the  aggregates  composed 
of  them. 

While  the  relatively  great  inertia  of  these  large  and  com- 
plex organic  atoms,  renders  them  comparativelj"  incapable 
of  being  set  in  motion  by  the  ethereal  undulations,  and  so  re- 


24  THE    DATA    OF    BIOLOGY. 

duced  to  less  coherent  forms  of  aggregation ;  there  is  reason 
to  think  that  this  same  inertia  facilitates  changes  of  arrange- 
ment among  their  constituent  atoms;  since,  in  proportion  as 
an  incident  force  impresses  but  little  motion  on  a  mass,  it  is 
the  better  able  to  impress  motion  on  the  parts  of  the  mass  in 
relation  to  each  other.  And  it  is  further  probable  that  the 
extreme  contrasts  in  molecular  mobilities  among  the  compo- 
nents of  these  highly  complex  atoms,  aid  in  producing  modi- 
liability  of  arrangement  among  them. 

Lastly,  the  great  difference  in  diiiusibility  between  colloids 
and  crystalloids,  makes  possible  in  the  tissues  of  organisms, 
a  specially  rapid  re-distribution  of  matter  and  motion  ;  both 
because  colloids,  being  easily  permeable  by  crystalloids,  can 
be  chemically  acted  on  throughout  their  whole  mass,  in- 
stead of  only  on  their  surfaces  ;  and  because  the  products  of 
decomposition,  being  also  crystalloids,  can  escape  as  fast  as 
they  are  produced,  leaving  room  for  further  like  transforma- 
tions. So  that  while  the  composite  atoms  of  which  organic 
tissues  are  built  up,  possess  that  low  molecular  mobility  fit- 
ting them  for  plastic  purposes,  it  results  from  the  extreme 
molecular  mobilities  of  their  ultimate  constituents,  that  the 
waste  products  of  vital  activity  escape  as  fast  as  they  are 
formed. 

To  all  which  add,  that  the  state  of  warmth,  or  increased 
molecular  vibration,  in*  which  all  the  higher  organisms  are 
kept,  increases  these  various  facilities  for  re-distribution  :  not 
only  as  aiding  chemical  changes,  but  as  accelerating  the  dif- 
fusion of  crystalloid  substances. 


ff.  C  State  CM** 


CHAPTER  II. 

THE  ACTIONS   OF  FOKCES   ON   OKGANIC   MATTER. 

§  10.  To  some  extent,  the  parts  of  every  body  are  changed 
in  their  arrangement  by  any  incident  mechanical  force. 
But  in  organic  bodies,  the  changes  of  arrangement  produced 
by  mechanical  forces  are  usually  conspicuous.  It  is  a  dis- 
tinctive mark  of  colloids,  that  they  yield  with  great  readiness 
to  pressures  and  tensions ;  and  that  they  yet  recover,  more 
or  less  completely,  their  original  shapes,  when  the  pres- 
sures or  tensions  cease.  It  is  clear  that  without  this 
pliability  and  elasticity,  most  organic  actions  would  be  im- 
possible. Not  only  temporary  but  permanent  alter- 
ations of  form  are  facilitated  by  this  colloid  character  of 
organic  matter.  Continued  pressure  on  living  tissue,  by 
modifying  the  processes  going  on  in  it,  (perhaps  retarding 
the  absorption  of  new  material  to  replace  the  old  that  has 
decomposed  and  diffused  away,)  gradually  diminishes  and 
finally  destroys  its  power  of  resuming  the  outline  it  had  at 
first.  Thus  the  matter  of  which  organisms  are  built  up,  is 
modifiable  by  arrested  momentum  or  by  continuous  strain, 
in  a  far  greater  degree  than  is  ordinary  matter. 

§  11.  Sensitiveness  to  certain  forces  that  are  quasi- 
mechanical,  if  not  mechanical  in  the  usual  sense,  is  seen  in 
two  closely-related  peculiarities  displayed  by  organic  matter 

3  25 


26  THE    DATA    OF   BIOLOGY. 

as  well  as  other  matter  that  assumes  the  same  state  of  mole- 
cular aggregation. 

Colloids  take  up  by  a  power  that  has  been  called  "  capillary 
affinity,"  a  large  quantity  of  water :  undergoing  at  the  same 
time  great  increase  of  bulk  with  change  of  form.  Conversely, 
with  like  readiness,  they  give  up  this  water  by  evaporation  : 
resuming  more  or  less  completely  their  original  states. 
Whether  resulting  from  capillarity,  or  from  the  relatively 
great  diffusibility  of  water,  or  from  both  ;  these  changes 
are  to  be  here  noted  as  showing  another  mode  in  which 
the  arrangement  of  parts  in  organic  bodies,  is  affected  by 
mechanical  forces. 

In  what  is  called  osmose,  we  have  a  further  mode  of  allied 
kind.  When  on  opposite  sides  of  a  permeable  septum,  and 
especially  a  septum  of  colloidal  substance,  are  placed  miscible 
solutions  of  different  densities,  a  double  transfer  takes  place  : 
a  large  quantity  of  the  less  dense  solution  finds  its  way  through 
the  septum  into  the  more  dense  solution ;  and  a  small  quan- 
tity of  the  more  dense  finds  its  way  into  the  less  dense — one 
result  being  a  considerable  increase  in  the  bulk  of  the  more 
dense  at  the  expense  of  the  less  dense.  This  process,  which 
appears  to  depend  on  several  conditions,  is  not  yet  fully  un- 
derstood. But  be  the  explanation  what  it  may,  the  process 
is  one  that  tends  continually  to  work  alterations  in  organic 
bodies.  Through  the  surfaces  of  plants  and  animals,  transfers 
of  this  kind  are  ever  taking  place.  Very  many  of  the  con- 
spicuous changes  of  form  undergone  by  organic  germs,  are 
due  mainly  to  the  permeation  of  their  limiting  membranes 
by  the  surrounding  liquids. 

It  should  be  added  that  besides  the  direct  alterations  which 
the  imbibition  and  transmission  of  water  and  watery  solutions 
by  colloids  produce  in  organic  matter,  they  produce  indirect 
alterations.  Being  instrumental  in  conveying  into  the  tissues 
the  agents  of  chemical  change,  and  conveying  out  of  them 
the  products  of  chemical  change,  they  aid  in  carrying  on 
other  re-distributions. 


THE    ACTIONS    OF    FORCES    ON    ORGANIC    MATTER.  27 

§  12.  As  elsewhere  shown  {First  Principles,  §  103)  Heat,  or 
a  raised  state  of  molecular  vibration,  enables  incident  forces 
more  easily  to  produce  changes  of  molecular  arrangement  in 
organic  matter.  But  besides  this,  it  conduces  to  certain  vital 
changes  in  so  direct  a  way  as  to  become  their  chief  cause. 

The  power  of  the  organic  colloids  to  imbibe  water,  and  to 
bring  along  with  it  into  their  substance  the  materials  which 
work  transformations,  would  not  be  continuously  operative 
if  the  water  imbibed  were  to  remain.  It  is  because  it  escapes, 
and  is  replaced  by  more  containing  more  materials,  that  the 
succession  of  changes  is  maintained.  Among  the  higher 
animals  and  higher  plants  its  escape  is  facilitated  by  evapor- 
ation. And  the  rate  of  evaporation  is,  other  things  equal, 
determined  by  heat.  Though  the  current  of  sap  in 

a  tree  is  mainly  caused  by  some  action,  probably  osmotic, 
that  is  at  work  in  the  roots  ;  yet  the  loss  of  water  from 
the  surfaces  of  the  leaves,  and  the  consequent  absorption 
of  more  sap  into  the  leaves  by  capillary  attraction,  must 
largely  aid  the  circulation.  The  drooping  of  a  plant  when 
exposed  to  the  sunshine  while  the  earth  round  its  roots  is 
dry,  shows  us  how  evaporation  empties  the  sap-vessels ;  and 
the  quickness  with  which  a  withered  slip  revives  on  being 
placed  in  water,  shows  us  the  part  which  capillary  action 
plays.  In  so  far  then,  as  the  evaporation  from  a  plant's  sur- 
face helps  to  produce  currents  of  sap  through  the  plant, 
we  must  regard  the  heat  which  produces  this  evaporation 
as  a  part-cause  of  those  re-distributions  of  matter  which 
these  currents  effect.  In  terrestrial    animals,  heat 

similarly  aids  the  changes  that  are  going  on.  The  exha- 
lation of  vapour  from  the  lungs  and  the  surface  of  the  skin, 
forming  the  chief  escape  of  the  water  that  is  swallowed, 
conduces  to  the  maintenance  of  those  currents  through  the 
tissues,  without  which  the  functions  would  cease.  For 
though  the  vascular  system  distributes  nutritive  fluids  in 
ramiried  channels  through  the  body ;  yet  the  absorption  of 
these  fluids  into  tissues,  partly  depends  on  the  escape  of  fluids 


28  THE    DATA    OF    BIOLOGY. 

which  the  tissues  already  contain.  Hence,  to  the  extent  that 
such  escape  is  facilitated  by  evaporation,  and  this  evaporation 
facilitated  by  heat,  heat  becomes  an  agent  of  re-distribution 
in  the  animal  organism. 

§  13.  Light,  which  is  now  known  to  modify  many  inor- 
ganic compounds — which  works  those  chemical  changes 
utilized  in  photography,  causes  the  combination  of  certain 
gases,  alters  the  molecular  arrangements  of  many  crystals, 
and  leaves  traces  of  its  action  even  on  substances  that  are  ex- 
tremely stable, — may  be  expected  to  produce  marked  effects 
on  substances  so  complex  and  unstable  as  those  which  make 
up  organic  bodies.  It  does  produce  such  marked  effects ; 
and  some  of  them  are  among  the  most  important  that 
organic  matter  undergoes. 

The  molecular  changes  wrought  by  light  in  animals,  are 
but  of  secondary  moment.  There  is  the  darkening  of  the 
skin  that  follows  exposure  to  the  sun's  rays.  There  are 
those  alterations  in  the  retina  which  cause  in  us  sensations 
of  colours.  And  on  certain  eyeless  creatures  that  are  semi- 
transparent,  the  light  permeating  their  substance  works 
some  effect  evinced  by  movement.  But  speaking  generally, 
the  opacity  of  animals  limits  the  action  of  light  to  their 
surfaces  ;  and  so  renders  its  direct  physiological  influence 
but  small.*  On  plants,  however,  the  solar  rays  that 

produce  in  us  the  impression  of  yellow,  are  the  immediate 
agents  of  those  molecular  changes  through  which  are  hourly 
accumulated  the  materials  for  further  growth.  Experiments 
have  shown  that  when  the  sun  shines  on  living  leaves,  they 
begin  to  exhale  oxygen  and  to  accumulate  carbon  and 
hydrogen — results  which  are  traced  to  the  decomposition  by 
the  solar  rays,  of  the  carbonic  acid  and  water  absorbed. 
It  is  now  an  accepted  conclusion  that,  by  the  help  of  certain 

*  The  increase  01  respiration  found  to  result  from  the  presence  of  light,  is 
probably  an  indirect  effect.  ±x  is  most  likely  due  to  the  recention  of  more  viviu 
impressions  through  the  eyes,  and  to  the  consequent  nervous  stimulation. 


THE    ACTIONS   OF    FORCES   ON   ORGANIC    MATTER.  29 

classes  of  the  ethereal  undulations  penetrating  their  leaves, 
plants  are  enabled  to  separate  from  the  associated  oxygen, 
those  two  elements  of  which  their  tissues  are  chiefly  built 
up. 

This  transformation  of  ethereal  undulations  into  certain 
molecular  re-arrangements  of  an  unstable  kind,  on  the  over- 
throw of  which  the  stored-up  forces  are  liberated  in  new 
forms,  is  a  process  that  underlies  all  organic  phenomena.  It 
will  therefore  be  well,  if  we  pause  a  moment  to  consider  whe- 
ther any  proximate  interpretation  of  it  is  possible.  Certain 
recent  researches  in  molecular  physics,  give  us  some  clue  to 
its  nature. 

The  elements  of  the  problem  are  these  : — The  atoms  of 
several  ponderable  matters  exist  in  combination  :  those  that 
are  combined  having  strong  affinities,  but  having  also  affin- 
ities less  strong  for  some  of  the  surrounding  atoms  that  are 
otherwise  combined.  The  atoms  thus  united,  and  thus  mixed 
among  others  with  which  they  are  capable  of  uniting,  are 
exposed  to  the  undulations  of  a  medium  that  is  relatively  so 
rare  as  to  seem  imponderable.  These  undulations  are  of 
numerous  kinds  :  they  differ  greatly  in  their  lengths,  or  in 
the  frequency  with  which  they  recur  at  any  given  point. 
And  under  the  influence  of  undulations  of  a  certain  frequency, 
some  of  these  atoms  are  transferred  from  atoms  for  which  they 
have  a  stronger  affinity,  to  atoms  for  which  they  have  a  weaker 
affinity.  That  is  to  say,  particular  orders  of  waves  of  a  rela- 
tively imponderable  matter,  remove  particular  atoms  of  pon- 
derable matter  from  their  attachments,  and  carry  them  within 
reach  of  other  attachments.  Now  the  discoveries  of 

Bunsen  and  Kirchoff  respecting  the  absorption  of  particular 
luminiferous  undulations  by  the  vapours  of  particular  sub- 
stances, joined  with  Prof.  Tyndall's  discoveries  respecting 
the  absorption  of  heat  by  gases,  show  very  clearly  that  the 
atoms  of  each  substance  have  a  rate  of  vibration  in  harmony 
with  ethereal  waves  of  a  certain  length,  or  rapidity  of  recur- 
rence.    Every  special  kind  of  atom  can  be  made  to  oscillate 


30  THE   DATA   OF   BIOLOGY. 

by  a  special  order  of  ethereal  waves,  which  are  absorbed  in 
producing  its  oscillations ;  and  can  by  its  oscillations  generate 
this  same  order  of  ethereal  waves.  Whence  it  appears  that 
immense  as  is  the  difference  in  density  between  ether  and 
ponderable  matter,  the  waves  of  the  one  can  set  the  atoms  of 
the  other  in  motion,  when  the  successive  impacts  of  the  waves 
are  so  timed  as  to  correspond  with  the  oscillations  of  the 
atoms.  The  effects  of  the  waves  are,  in  such  case,  cumula- 
tive; and  each  atom  gradually  acquires  a  momentum  made  up 
of  countless  infinitesimal  momenta.  Note  further, 

that  unless  the  members  of  a  chemically-compound  atom  are 
so  bound  up  as  to  be  incapable  of  any  relative  movements  (a 
supposition  at  variance  with  the  conceptions  of  modern  science) 
we  must  conceive  them  as  severally  able  to  vibrate  in  unison 
or  harmony  with  those  same  classes  of  ethereal  waves  that 
affect  them  in  their  uncombined  states.  While  the  compound 
atom  as  a  whole,  will  have  some  new  rate  of  oscillation  de- 
termined by  its  attributes  as  a  whole ;  its  components  will 
retain  their  original  rates  of  oscillation,  subject  only  to  modifi- 
cations by  mutual  influence.  Such  being  the  cir- 
cumstances of  the  case,  we  may  partially  understand  how 
the  sun's  rays  can  effect  chemical  decompositions.  If  the 
members  of  a  binary  atom  stand  so  related  to  the  undulations 
falling  on  them,  that  one  is  thrown  into  a  state  of  increased 
oscillation  and  the  other  not ;  it  is  manifest  that  there 
must  arise  a  tendency  towards  the  dislocation  of  the  two — a 
tendency  which  may  or  may  not  take  effect,  according  to  the 
weakness  or  strength  of  their  union,  and  according  to  the 
presence  or  absence  of  collateral  affinities.  This  inference  is 
in  harmony  with  several  significant  facts.  Dr.  Draper 
remarks  that  "  among  metallic  substances  (compounds)  those 
first  detected  to  be  changed  by  light,  such  as  silver,  gold, 
mercury,  lead,  have  all  high  atomic  weights ;  and  such  as 
sodium  and  potassium,  the  atomic  weights  of  which  are  low, 
appeared  to  be  less  changeable."  As  here  interpreted,  the 
fact   specified  amounts  to  this ;   that  the  compounds  most 


THE   ACTIONS    OF    FORCES    ON   ORGANIC   MATTER.  31 

readily  decomposed  by  light,  are  those  in  which  there 
is  a  marked  contrast  between  the  atomic  weights  of  the 
constituents,  and  probably  therefore  a  marked  contrast 
between  the  rapidities  of  their  vibrations.  The  circumstance, 
too,  that  different  chemical  compounds  are  decomposed  or 
modified  in  different  parts  of  the  spectrum,  implies  that  there 
is  a  relation  between  special  orders  of  undulations  and  special 
orders  of  composite  atoms — doubtless  a  correspondence 
between  the  rates  of  these  undulations  and  the  rates  of 
oscillation  which  some  of  the  components  of  such  atoms 
will  assume.  Strong  confirmation  of  this  view  may 

be  drawn  from  the  decomposing  actions  of  those  longer 
ethereal  waves  which  we  perceive  as  heat.  On  contemplating 
the  whole  series  of  binary  compounds,  we  see  that  the  ele- 
ments which  are  most  remote  in  their  atomic  weights,  as 
hvdrogen  and  the  noble  metals,  will  not  combine  at  all :  their 
vibrations  are  so  unlike  that  they  cannot  keep  together 
under  any  conditions  of  temperature.  If  again  we  look  at  a 
smaller  group,  as  the  metallic  oxides,  we  see  that  whereas 
those  metals  that  have  atoms  nearest  in  weight  to  the  atoms 
of  oxygen,  cannot  be  separated  from  oxygen  by  heat,  even 
when  it  is  joined  by  a  powerful  collateral  affinity  ;  those 
metals  which  differ  more  widely  from  oxygen  in  their  atomic 
weights,  can  be  de-oxidized  by  carbon  at  high  temperatures ; 
and  those  which  differ  from  it  most  widely,  combine  with  it 
very  reluctantly,  and  yield  it  up  if  exposed  to  thermal  undu- 
lations of  moderate  intensity.  And  here  indeed,  remem- 
bering the  relations  among  the  atomic  weights  in  the  two 
eases,  may  we  not  suspect  a  close  analogy  between  the  de- 
oxidation  of  a  metallic  oxide  by  carbon  under  the  influence 
of  the  longer  ethereal  waves,  and  the  de-carbonization  of 
carbonic  acid  by  hydrogen  under  the  influence  of  the  shorter 
ethereal  waves  ? 

These  conceptions  help  us  to  some  dim  notion  of  the  mode 
in  which  changes  are  wrought  by  light  in  the  leaves  of  plants. 
Among  the  several  elements  concerned,  there  are  wide  differ- 


32  THE   DATA   OF   BIOLOGY. 

ences  in  molecular  mobility,  and  probably  in  the  rates  of 
molecular  vibration.  Each  is  combined  with  one  of  the  others ; 
but  is  capable  of  forming  various  combinations  with  the  rest. 
And  they  are  severally  in  presence  of  a  complex  compound 
into  which  they  all  enter,  and  which  is  ready  to  assimilate 
with  itself  the  new  compound  atoms  that  they  form.  Certain 
of  the  ethereal  waves  falling  on  them  when  thus  arranged, 
there  results  a  detachment  of  some  of  the  combined  atoms 
and  a  union  of  the  rest.  And  the  conclusion  suggested  is, 
that  the  induced  vibrations  among  the  various  atoms  as  at 
first  arranged,  are  so  incongruous  as  to  produce  instability ; 
and  to  give  collateral  affinities  the  power  to  work  a  re- 
arrangement, which,  though  less  stable  under  other  conditions, 
is  more  stable  in  the  presence -of  these  particular  undula- 
tions. There  seems,  indeed,  no  choice  but  to  conceive 
the  matter  thus.  An  atom  united  with  one  for  which  it  has 
a  strong  affinity,  has  to  be  transferred  to  another  for  which 
it  has  a  weaker  affinity.  This  transfer  implies  motion.  The 
motion  is  given  by  the  waves  of  a  medium  that  is  relatively 
imponderable.  No  one  wave  of  this  imponderable  medium 
can  give  the  requisite  motion  to  this  atom  of  ponderable 
matter :  especially  as  the  atom  is  held  by  a  positive  force  besides 
its  inertia.  The  motion  required  can  hence  be  given  only 
by  successive  waves ;  and  that  these  may  not  destroy  each 
other's  effects,  it  is  needful  that  each  shall  strike  the  atom 
just  when  it  has  completed  that  recoil  produced  by  the  impact 
of  previous  ones.  That  is,  the  ethereal  undulations  must 
coincide  in  rate  with  the  oscillations  of  the  atom,  determined 
by  its  inertia  and  the  forces  acting  on  it.  It  is  also  requisite 
that  the  rate  of  oscillation  of  the  atom  to  be  detached,  shall 
differ  from  that  of  the  atom  with  which  it  is  united  ;  since 
if  the  two  oscillated  in  unison,  the  ethereal  waves  would  not 
tend  to  separate  them.  And,  finally,  the  successive  impacts 
of  the  ethereal  waves  must  be  accumulated,  until  the  resulting 
oscillations  have  become  so  wide  in  their  sweep  as  greatly  to 
weaken  the  cohesion  of  the  united  atoms,  at  the  same  time 


THE    ACTIONS   OF    FORCES    ON    ORGANIC   MATTER.  33 

that  they  bring  one  of  them  within  reach  of  other  atoms  with 
which  it  will  combine.  In  this  way  only  does  it  seem  possible 
for  such  a  force  to  produce  such  a  transfer.  More- 

over, while  we  are  thus  enabled  to  conceive  how  light  may 
work  the*e  molecular  changes;  we  also  gain  an  insight  into 
the  method  by  which  the  insensible  motions  propagated  to 
us  from  the  sun,  are  treasured  up  in  such  way  as  afterwards 
to  generate  sensible  motions.  Bv  the  accumulation  of  in- 
finitesimal  impacts,  atoms  of  ponderable  matter  are  made  to 
oscillate.  The  quantity  of  motion  which  each  of  them 
eventually  acquires,  effects  its  transfer  to  a  position  of  un- 
stable equilibrium,  from  which  it  can  afterwards  be  readily 
dislodged.  And  when  so  dislodged,  along  with  other  atoms 
similarly  and  simultaneously  affected,  there  is  suddenly  given 
out  all  the  motion  which  had  been  before  impressed  on  it. 

Speculation  aside,  however,  that  which  it  concerns  us  to 
notice,  is  the  broad  fact  that  light  is  an  all-important  agent 
of  molecular  changes  in  organic  substances.  It  is  not  here 
necessary  for  us  to  ascertain  how  light  produces  these  compo- 
sitions and  decompositions  :  it  is  necessary  only  for  us  to 
observe  that  it  does  produce  them.  That  the  characteristic 
matter  called  chlorophyll,  which  gives  the  green  colour  to 
leaves,  makes  its  appearance  whenever  the  blanched  shoots  of 
plants  are  exposed  to  the  sun ;  that  the  petals  of  flowers, 
uncoloured  while  in  the  bud,  acquire  their  bright  tints  as 
they  unfold  ;  and  that  on  the  outer  surfaces  of  animals, 
analogous  changes  are  induced ;  are  wide  inductions  which 
are  enough  for  our  present  purpose. 

§  14.  "We  come  next  to  the  agency  of  chief  importance 
among  those  that  work  changes  in  organic  matter ;  namely, 
chemical  affinity.  How  readily  vegetal  and  animal  substances 
are  modified  by  other  substances  put  in  contact  with  them, 
we  see  daily  illustrated.  Besides  the  many  compounds  which 
cause  the  death  of  an  organism  into  which  they  are  put,  we 
have  the  much  greater  number  of  compounds  which  work 


34  THE   DATA    OF   BIOLOGY. 

those  milder  effects  termed  medicinal — effects  implying,  like 
the  others,  molecular  re-arrangements.  Indeed,  nearly  all 
soluble  chemical  compounds,  natural  and  artificial,  produce, 
when  taken  into  the  body,  alterations  that  are  more  or  less 
conspicuous  in  their  results. 

After  what  was  shown  in  the  last  chapter,  it  will  be  mani- 
fest that  this  extreme  modifiability  of  organic  matter  by 
chemical  agencies,  is  the  chief  cause  of  that  active  molecular 
re-arrangement  which  organisms,  and  especially  animal  or- 
ganisms, display.  In  the  two  fundamental  functions  of 
nutrition  and  respiration,  we  have  the  means  by  which  the 
supply  of  materials  for  this  active  molecular  re-arrangement 
is  maintained. 

Thus  the  process  of  animal  nutrition  consists  in  the  absorp- 
tion, partly  of  those  complex  substances  that  are  thus  highly 
capable  of  being  chemically  altered,  and  partly  in  the  absorp- 
tion of  simpler  substances  capable  of  chemically  altering 
them.  The  tissues  always  contain  small  quantities  of  alka- 
line and  earthy  salts,  which  enter  the  system  in  one  form 
and  are  excreted  in  another.  Though  we  do  not  know  spe- 
cifically the  parts  which  these  salts  play,  yet  from  their 
universal  presence,  and  from  the  transformations  which  they 
undergo  in  the  body,  it  may  be  safely  inferred  that  their 
chemical  affinities  are  instrumental  in  working  some  of  the 
metamorphoses  ever  going  on. 

The  inorganic  substance,  however,  on  which  mainly  depend 
these  metamorphoses  in  organic  matter,  is  not  swallowed 
along  with  the  solid  and  liquid  food,  but  is  absorbed  from 
the  surrounding  medium — air  or  water,  as  the  case  may  be. 
Whether  the  oxygen  taken  in,  either,  as  by  the  lowest 
animals,  through  the  general  surface,  or,  as  by  the  higher 
animals,  through  respiratory  organs,  is  the  immediate  cause 
of  those  molecular  changes  that  are  ever  going  on  through- 
out the  living  tissues ;  or  whether  the  oxygen,  playing  the 
part  of  scavenger,  merely  aids  these  changes  by  carrying 
away  the  products  of  decompositions  otherwise  caused ;  it 


THE    ACTIONS    OF    FORCES    ON   ORGANIC   MATTER.  35 

equally  remains  true,  that  these  changes  are  maintained  by 
its  instrumentality.  Whether  the  oxygen  absorbed  and 
diffused  through  the  system,  effects  a  direct  oxidation  of  the 
organic  colloids  which  it  permeates ;  or  whether  it  first  leads 
to  the  formation  of  simpler  and  more  oxidized  compounds, 
that  are  afterwards  further  oxidized  and  reduced  to  still 
simpler  forms  ;  matters  not,  in  so  far  as  the  general  result  is 
concerned.  In  any  case  it  holds  good,  that  the  substances 
of  which  the  animal  body  is  built  up,  enter  it  in  a  but 
slightly  oxidized  and  highly  unstable  state ;  while  the  great 
mass  of  them  leave  it  in  a  fully  oxidized  and  stable  state. 
It  follows,  therefore,  that  whatever  the  special  changes  gone 
through,  the  general  process  is  a  falling  from  a  state  of  un- 
stable chemical  equilibrium,  to  a  state  of  stable  chemical 
equilibrium.  Whether  this  process  be  direct  or  indirect, 
the  total  molecular  re-arrangement  and  the  total  motion 
given  out  in  effecting  it,  must  be  the  same. 

§  15.  There  is  another  species  of  re-distribution  among 
the  component  units  of  organisms,  which  is  not  immediately 
effected  by  the  affinities  of  the  units  concerned,  but  is  me- 
diately effected  by  other  affinities  ;  and  there  is  reason  to 
think  that  the  re-distribution  thus  caused,  is  important  in 
amount,  if  not  indeed  the  most  important.  In  ordinary  cases 
of  chemical  action,  the  two  or  more  substances  concerned, 
themselves  undergo  changes  of  molecular  arrangement ;  and 
the  changes  are  confined  to  the  substances  themselves.  But 
there  are  other  cases  in  which  the  chemical  action  going  on, 
does  not  end  with  the  substances  at  first  concerned  ;  but  sets 
going  chemical  actions,  or  changes  of  molecular  arrangement, 
among  surrounding  substances  that  would  else  remain  qui- 
escent. And  there  are  yet  further  cases  in  which  mere 
contact  with  a  substance  that  is  itself  quiescent,  will  cause 
other  substances  to  undergo  rapid  metamorphoses.  In 

what  we  call  fermentation,  the  first  species  of  this  communi- 
cated chemical  action  is   exemplified.     One   part  of  yeast, 


36  THE   DATA   OF   BIOLOGY. 

while  itself  undergoing  molecular  changes,  will  convert  100 
parts  of  sugar  into  alcohol  and  carbonic  acid  ;  and  during  its 
own  decomposition,  one  part  of  diastase  "  is  able  to  effect  the 
transformation  of  more  than  1000  times  its  weight  of  starch 
into  sugar."  As  illustrations  of  the  second  species, 

may  be  mentioned  those  changes  which  are  suddenly  produced 
in  many  colloids  by  minute  portions  of  various  substances 
added  to  them — substances  that  are  not  undergoing  any 
manifest  transformation,  and  suffer  no  appreciable  effect 
from  the  contact.  The  nature  of  the  first  of  these  two 

kinds  of  communicated  molecular  change,  which  here  chiefly 
concerns  us,  may  be  rudely  represented  by  certain  visible 
changes  that  are  communicated  from  mass  to  mass,  when  a 
series  of  masses  has  been  arranged  in  a  special  way.  The 
simplest  example  is  that  furnished  by  the  child's  play  of 
setting  bricks  on  end  in  a  row,  in  such  positions  that  when 
the  first  is  overthrown  it  overthrows  the  second ;  the  second, 
the  third ;  the  third,  the  fourth ;  and  so  on  to  the  end  of  the 
row.  Here  we  have  a  number  of  units  severally  placed  in 
unstable  equilibrium,  and  in  such  relative  positions  that  each, 
while  falling  into  a  state  of  stable  equilibrium,  gives  an  im- 
pulse to  the  next,  sufficient  to  make  the  next,  also,  fall  from 
unstable  to  stable  equilibrium.  Now  since  among  mingled 
compound  atoms,  no  one  can  undergo  change  in  the  arrange- 
ment of  its  parts  without  a  molecular  motion  that  must  cause 
some  disturbance  all  around  ;  and  since  an  adjacent  atom 
disturbed  by  this  communicated  motion,  may  have  the  arrange 
ment  of  its  constituent  molecules  altered,  if  it  is  not  a  stable 
arrangement ;  and  since  we  know,  both  that  the  atoms  which 
are  changed  by  this  so-called  catalysis  are  unstable,  and  that 
the  atoms  resulting  from  their  change  are  more  stable ;  it 
seems  probable  that  the  transformation  is  really  analogous, 
in  principle,  to  the  familiar  one  named.  "Whether  thus 
interpretable  or  not,  however,  there  is  great  reason  for  think- 
ing that  to  this  kind  of  action,  is  due  a  large  amount  of  vital 


THE    ACTIONS   OF    FORCES    OX   ORGANIC    MATTER.  37 

metamorphosis.  Let  us  contemplate  the  several  groups  of 
facts  which  point  to  this  conclusion. 

In  the  last  chapter  (§  2)  we  incidentally  noted  the  extreme 
instability  of  nitrogenous  compounds  in  general.  We  saw 
that  sundry  of  them  are  liable  to  explode  on  the  slightest 
incentive — sometimes  without  any  apparent  cause  ;  and  that 
of  the  rest,  the  great  majority  are  very  easily  decomposed  by 
heat,  and  by  other  substances.  We  shall  perceive  much 
significance  in  this  general  characteristic,  when  we  join  it 
with  the  fact,  that  the  substances  capable  of  initiating  extensive 
molecular  changes  in  the  manner  above  described,  are  all 
nitrogenous  ones.  Yeast  consists  of  vegetal  cells  containing 
nitrogen, — cells  that  grow  by  assimilating  the  nitrogenous 
matter  contained  in  wort.  Similarly,  the  "  vinegar-plant," 
which  so  greatly  facilitates  the  formation  of  acetic  acid  from 
alcohol,  is  a  fungoid  growth,  that  is  doubtless,  like  others  of 
its  class,  rich  in  nitrogenous  compounds.  Diastase,  by  which 
the  transformation  of  starch  into  sugar  is  effected,  during 
the  process  of  malting,  is  also  a  nitrogenous  body.  So  too 
is  a  substance  called  synaptase — an  albumenous  principle 
contained  in  almonds,  that  has  the  power  of  working  several 
metamorphoses  in  the  matters  associated  with  it.  These 
nitrogenized  compounds,  like  the  rest  of  their  family,  are 
remarkable  for  the  rapidity  with  which  they  decompose  ;  and 
the  extensive  changes  produced  by  them  in  the  accompanying 
oxy-hydro-carbons,  are  found  to  vary  in  their  kinds  accord- 
ing as  the  decompositions  of  the  ferments  vary  in  their 
stages.  We   have   next   to   note,  as   having  here   a 

meaning  for  us,  the  chemical  contrasts  between  those  organ- 
isms which  carry  on  their  functions  by  the  help  of  external 
forces,  and  those  which  carry  on  their  functions  by  forces 
evolved  from  within.  If  we  compare  animals  and  plants,  we 
see  that  whereas  plants,  characterized  as  a  class  by  containing 
but  little  nitrogen,  are  dependent  on  the  solar  rays  for  their 
vital  activities ;  animals,  the  vital  activities  of  which  are  not 


38  THE    DATA    OF    BIOLOGY. 

thus  dependent,  mainly  consist  of  nitrogenous  substances. 
There  is  one  marked  exception  to  this  broad  distinction,  how- 
ever; and  this  exception  is  specially  instructive.  Among 
plants,  there  is  a  considerable  group — the  Fungi — many  mem- 
bers of  which,  if  not  all,  can  live  and  grow  in  the  dark ;  and 
it  is  their  peculiarity  that  they  are  very  much  more  nitro- 
genous than  other  plants.  Yet  a  third  class  of  facts 
of  like  significance,  is  disclosed  when  we  compare  different 
portions  of  the  same  organisms.  The  seed  of  a  plant  contains 
nitrogenous  substance  in  a  far  higher  ratio  than  the  rest  of 
the  plant ;  and  the  seed  differs  from  the  rest  of  the  plant  in 
its  ability  to  initiate,  in  the  absence  of  light,  extensive  vital 
changes — -the  changes  constituting  germination.  Similarly 
in  the  bodies  of  animals,  those  parts  which  carry  on  active 
functions  are  nitrogenous ;  while  parts  that  are  non-nitro- 
genous— as  the  deposits  of  fat— carry  on  no  active  functions. 
And  we  even  find  that  the  appearance  of  non-nitrogenous 
matter,  throughout  tissues  normally  composed  almost  wholly 
of  nitrogenous  matter,  is  accompanied  by  loss  of  activity : 
what  is  called  fatty  degeneration,  being  the  concomitant  of 
failing  vitality.  One  more  fact  which  serves  to  make 
still  clearer  the  meaning  of  the  foregoing  ones,  still  remains — 
the  fact,  namely,  that  in  no  part  of  any  organism  where  vital 
changes  are  going  on,  is  nitrogenous  matter  wholly  absent. 
It  is  common  to  speak  of  plants — or  at  least  all  parts  of 
plants  but  the  seeds — as  non-nitrogenous.  But  they  are  only 
relatively  so ;  not  absolutely.  The  quantity  of  albumenoid 
substance  contained  in  the  tissues  of  plants,  is  extremely  small 
compared  with  the  quantity  contained  in  the  tissues  of  ani- 
mals ;  but  all  plant-tissues  which  are  discharging  active 
functions,  contain  some  albumenoid  substance.  In  every 
living  vegetal  cell  there  is  a  certain  part  that  contains  nitro- 
gen. This  part  initiates  those  changes  which  constitute  the 
development  of  the  cell.  And  if  it  cannot  be  said  that  the 
primordial  utricle,  as  this  nitrogenous  part  is  called,  is  the 
worker  of  all  subsequent  changes  undergone  by  the  cell,  it 


THE   ACTIONS    OF    FORCES   ON    OEGANIC    MATTER.  39 

nevertheless  continues  to  be  the  part  in  which  the  independent 
activity  is  most  marked. 

Looking  at  the  evidence  thus  brought  together,  do  we 
not  get  an  insight  into  the  part  played  by  nitrogenous 
matter  in  organic  changes  ?  We  see  that  nitrogenous  com- 
pounds in  general,  are  extremely  prone  to  decompose :  their 
decomposition  often  involving  a  sudden  and  great  evolution 
of  force.  We  see  that  the  substances  classed  as  ferments, 
which,  during  their  own  molecular  changes,  set  up  molecular 
changes  in  the  accompanying  oxy-hydro  carbons,  are  all 
nitrogenous.  We  see  that  among  classes  of  organisms,  and 
among  the  parts  of  each  organism,  there  is  a  relation  between 
the  amount  of  nitrogenous  matter  present  and  the  amount  of 
independent  activity.  And  we  see  that  even  in  organisms 
and  parts  of  organisms  where  the  activity  is  least,  such 
changes  as  do  take  place  are  initiated  by  a  substance  contain- 
ing nitrogen.  Does  it  not  seem  probable,  then,  that  these 
extremely  unstable  compounds,  have  everywhere  the  effect  of 
communicating  to  the  less  unstable  compounds  associated 
with  them,  molecular  movements  towards  a  stable  state,  like 
those  they  are  themselves  undergoing  ?  The  changes  which 
we  thus  suppose  nitrogenous  matter  to  produce  in  a  body, 
are  clearly  analogous  to  those  which  we  see  it  produce  out  of 
the  body.  Out  of  the  body,  certain  oxy-hydro-carbons  in  con- 
tinued contact  with  nitrogenous  matter,  are  transformed  into 
carbonic  acid  and  alcohol,-  and  unless  prevented  the  alcohol 
is  transformed  into  acetic  acid  :  the  substances  formed  being 
thus  more  highly  oxidized  and  more  stable  than  the  substances 
destroyed.  In  the  body,  these  same  oxy-hydro-carbons 
together  with  some  hydro-carbons,  in  continued  contact  with 
nitrogenous  matter,  are  transformed  into  carbonic  acid  and 
water :  substances  which  are  also  more  highly  oxidized  and 
more  stable  than  those  from  which  they  result.  And  since 
acetic  acid  is  itself  resolved  by  further  oxidation  into  carbonic 
acid  and  water  ;  we  see  that  the  chief  difference  between  the 
two  cases,  is,  that  the  process  is  more  completely  effected  in 


40  THE   DATA    OF   BIOLOGY. 

the  bodj^,  than  it  is  out  of  the  body.*  Thus,  to  carry  further  the 
simile  used  above,  the  atoms  of  hydro-carbons  and  oxy-hydro- 
carbons  contained  in  the  tissues,  are,  like  bricks  on  end,  not  in 
the  stablest  equilibrium,  but  still  in  an  equilibrium  so  stable, 
that  they  cannot  be  overthrown  by  the  chemical  and  thermal 
forces  which  the  body  brings  to  bear  on  them.  On  the  other 
hand,  being  like  similarly-placed  bricks  that  have  very  nar- 
row ends,  the  nitrogenous  atoms  contained  in  the  tissues  are 
in  so  unstable  an  equilibrium  that  they  cannot  withstand 
these  forces.  And  when  these  delicately-poised  nitrogenous 
atoms  fall  into  stable  arrangements,  they  give  impulses  to 
the  more  firmly-poised  non-nitrogenous  atoms,  which  cause 
them  also  to  fall  into  stable  arrangements.  It  is  a 

curious  and  significant  fact,  that  in  the  arts,  we  not  only 
utilize  this  same  principle  of  initiating  extensive  changes 
among  comparatively  stable  compounds,  by  the  help  of  com- 
pounds much  less  stable ;  but  we  employ  for  the  purpose 
compounds  of  the  same  general  class.  Our  modern  method 
of  firing  a  gun,  is  to  place  in  close  proximity  with  the  gun- 
powder which  we  wish  to  decompose  or  explode,  a  small  por- 
tion of  fulminating  powder,  which  is  decomposed  or  exploded 
with  extreme  facility  ;  and  which,  on  decomposing,  communi- 
cates the  consequent  molecular  disturbance  to  the  less-easily 
decomposed  gunpowder.  When  we  ask  what  this  fulminating 
powder  is  composed  of,  we  find  that  it  is  a  nitrogenous  salt. 

Thus  various  evidences  point  to  the  conclusion,  that  besides 
the  molecular  re-arrangements  produced  in  organic  matter  by 
direct  chemical  action,  there  are  others  of  kindred  importance 
produced  by  indirect  chemical  action.     Indeed,  the  inference 

*  May  it  not  be  well  to  inquire  whether  alcohol  is  not,  in  a  greater  or  less 
measure,  transformed  in  the  body  into  acetic  acid  ?  If,  when  in  contact  with 
changing  nitrogenous  matter,  in  presence  of  oxygen,  alcohol  undergoes  this 
transformation  out  of  the  body,  it  seems  not  improbable  that  it  does  so  in  the  body 
— especially  as  the  raised  temperature  which  aids  the  change  in  the  one  case  exists 
in  the  other.  It  would  be  out  of  place  here  to  set  down  the  sundry  facts  which 
countenance  this  hypothesis.  I  may  say,  however,  that  it  apparently  removes 
some  of  the  difficulties  which  at  present  perplex  the  question. 


THE    ACTIONS    OF   FORCES    ON   ORGANIC   MATTER.  41 

that  some  of  the  leading  transformations  occurring  in  the 
animal  organism,  are  due  to  this  so-called  catalysis,  appears 
necessitated  by  the  general  aspect  of  the  facts  ;  apart  from 
any  such  detailed  interpretations  as  the  foregoing.  "We  know 
that  various  amylaceous  and  saccharine  matters  taken  as  food, 
are  decomposed  in  their  course  through  the  body.  We  know 
that  these  matters  do  not  become  components  of  the  tissues, 
but  only  of  the  fluids  circulating  through  them  ;  and  that 
thus  their  metamorphosis  is  not  an  immediate  result  of  the 
organic  activities.  We  know  that  their  stability  is  such  that 
the  thermal  and  chemical  forces  to  which  they  are  exposed 
in  the  body,  cannot  alone  decompose  them.  The  only  explan- 
ation open  to  us,  therefore,  is  that  the  transformation  of  these 
oxy-hydro-carbons,  into  carbonic  acid  and  water,  is  due  to 
communicated  chemical  action. 

§  16.  This  chapter  will  have  served  its  purpose  if  it  has 
given  a  conception  of  the  extreme  modifiability  of  organic 
matter  by  surrounding  agencies.  Even  did  space  permit, 
it  would  be  needless  to  describe  in  detail  the  immensely 
varied  and  complicated  changes  which  the  forces  from  mo- 
ment to  moment  acting  on  them,  work  in  living  bodies. 
Dealing  with  biology  in  its  general  principles,  it  concerns  us 
only  to  notice  how  specially  sensitive  are  the  substances  of 
which  organisms  are  built  up,  to  the  varied  influences  that 
act  upon  organisms.  And  their  special  sensitiveness  has  been 
made  sufficiently  manifest,  in  the  several  foregoing  sections. 


CHAPTER  III. 

THE  RE-ACTIONS   OF  ORGANIC   MATTER  ON  FORCES. 

§  17.  Re-distributions  of  Matter,  imply  concomitant  re- 
distributions of  Motion.  That  which  under  one  of  its  aspects 
we  contemplate  as  an  alteration  of  arrangement  among  the 
parts  of  a  body,  is,  under  a  correlative  aspect,  an  alteration 
of  arrangement  among  certain  momenta  whereby  these  parts 
are  impelled  to  their  new  positions.  At  the  same  time  that 
a  force,  acting  differently  on  the  different  units  of  an  aggre- 
gate, changes  their  relations  to  each  other  ;  these  units,  re- 
acting differently  on  the  different  parts  of  the  force,  work 
equivalent  changes  in  the  relations  of  these  to  one  another. 
Inseparably  connected  as  they  are,  these  two  orders  of  phe- 
nomena are  liable  to  be  confounded  together.  It  is  very 
needful,  however,  to  distinguish  between  them.  In  the  last 
chapter,  we  took  a  rapid  survey  of  the  re-distributions  which 
forces  produce  in  organic  matter  ;  and  here  we  must  take  a 
like  survey  of  the  simultaneous  re-distributions  undergone  by 
the  forces. 

At  the  outset  we  are  met  by  a  difficulty.  The  parts  of  an 
inorganic  mass  undergoing  re-arrangement  by  an  incident 
force,  are,  in  most  cases,  passive — do  not  complicate  those 
necessary  re-actions  that  result  from  their  inertia,  by  other 
forces  which  they  originate.  But  in  organic  matter,  the 
re-arranged  parts  do  not  re-act  in  virtue  of  their  inertia  only  ; 
they  are  so  constituted  that  the  incident  force  usually  sets  up 

42 


THE   RE-ACTIONS   OF   ORGANIC   MATTER   ON   FORCES.  43 

in  them  other  actions  which  are  much  more  important.  In- 
deed, what  we  may  call  the  indirect  re-actions  thus  caused, 
are  so  great  in  their  amounts  compared  with  the  direct  re- 
actions, that  they  quite  obscure  them. 

In  strictness,  these  two  kinds  of  re-action  should  not  be 
dealt  with  together.  The  impossibility  of  separating  them, 
however,  compels  us  to  disregard  the  distinction  between 
them.  Under  the  above  general  title,  we  must  include  both 
the  immediate  re-actions  and  those  re-actions  mediately 
produced,  which  are  among  the  most  conspicuous  of  vital 
phenomena. 

§  18.  From  organic  matter,  as  from  all  other  matter, 
incident  forces  call  forth  that  re-action  which  we  know  as 
heat.  More  or  less  of  molecular  vibration  almost  necessarily 
results,  when,  to  the  forces  at  work  among  the  molecules 
of  any  aggregate,  other  forces  are  added.  Experiment 
abundantly  demonstrates  this  in  the  case  of  inorganic 
masses  ;  and  it  must  equally  hold  in  the  case  of  organic 
masses.  In  both  cases  the  force  which,  more  mark- 

edly than  any  other,  produces  this  thermal  re-action,  is  that 
which  causes  the  union  of  different  substances  with  each 
other.  Though  inanimate  bodies  admit  of  being  greatly 
heated  by  pressure  and  by  the  electric  current,  yet  the 
evolutions  of  heat  thus  induced,  are  neither  so  common,  nor 
in  most  cases  so  conspicuous,  as  those  resulting  from  chemical 
combination.  And  though  in  animate  bodies,  there  are 
doubtless  certain  amounts  of  heat  generated  by  other  actions  ; 
yet  these  are  all  secondary  to  the  heat  generated  by  the 
action  of  oxygen  on  the  substances  composing  the  tissues  and 
the  substances  contained  in  them.  Here,  however, 

we  see  one  of  the  characteristic  distinctions  between  inani- 
mate and  animate  bodies.  Among  the  first,  there  are  but 
few  which  ordinarily  exist  in  a  condition  to  evolve  the  heat 
caused  by  chemical  combination  ;  and  such  as  are  in  this 
condition  soon  cease  to  be  so,  when  chemical  combination 


44  TIIE    DATA    OF   BIOLOGY. 

and  genesis  of  heat  once  begin  in  them.  Whereas  among 
the  second,  there  universally  exists  the  ability,  more  or  less 
decided,  thus  to  evolve  heat ;  and  the  evolution  of  heat,  in 
some  cases  very  slight  and  in  no  cases  very  great,  continues 
as  long  as  they  remain  animate  bodies. 

The  relation  between  active  change  of  matter  and  re-active 
genesis  of  atomic  vibration,  is  clearly  shown  by  the  contrasts 
between  different  organisms,  and  between  different  states  and 
parts  of  the  same  organism.  In  plants,  the  genesis  of  heat  is 
extremely  small,  in  correspondence  with  their  extremely 
small  production  of  carbonic  aid  :  those  portions  only,  as 
flowers  and  germinating  seeds,  in  which  considerable  oxidation 
is  going  on,  having  a  decidedly  raised  temperature.  Among 
animals,  we  see  that  the  hot-blooded  are  those  which  expend 
much  force  and  respire  actively.  We  see  that  though  such 
creatures  as  insects  are  scarcely  at  all  warmer  than  the  surround- 
ing air  when  they  are  still,  they  rise  several  degrees  above  it 
when  they  exert  themselves  ;  and  that  in  creatures  like  our- 
selves, which  habitually  maintain  a  heat  much  greater  than 
that  of  their  medium,  exercise  is  accompanied  by  an  ad- 
ditional production  of  heat,  often  to  an  inconvenient  extent. 

This  molecular  agitation  accompanying  the  molecular 
re-arrangements  that  are  caused  by  oxygen  taken  into  the 
animal  organism,  must  result  both  from  the  union  of  oxygen 
with  those  nitrogenous  matters  of  which  the  tissues  are 
composed,  and  from  its  union  with  those  non-nitrogenous 
matters  which  are  diffused  through  the  tissues.  Just  as  much 
heat  as  would  be  caused  by  the  oxidation  of  such  matters 
out'  of  the  body,  must  be  caused  by  their  oxidation  in  the 
body.  In  the  one  case  as  in  the  other,  the  heat  must  be  re- 
garded as  a  concomitant.  Whether  the  distinction 
made  by  Liebig  between  nitrogenous  substances  as  tissue- 
food,  and  non-nitrogenous  substances  as  heat-food,  be  true  or 
not  in  a  narrower  sense,  it  cannot  be  accepted  in  the  sense 
that  tissue-food  is  not  also  heat-food.  Indeed  he  does  not 
himself  assert  it  in  this  sense.     The  ability  of  carnivorous 


THE    RE-ACTIONS    OF    ORGANIC    MATTER    ON    FORCES.  4:5 

animals  to  live  and  generate  heat  while  consuming  matter  that 
is  almost  exclusively  nitrogenous,  to  say  nothing  of  the  con- 
stant relation  above  shown  between  functional  activity  and  the 
evolution  of  heat,  suffices  to  prove  that  the  nitrogenous  com- 
pounds forming  the  tissues  are  heat-producers,  as  well  as  the 
non-nitrogenous  compounds  circulating  among  and  through 
the  tissues.  But  it  is  possible  that  this  antithesis  is  not 

true  even  in  the  more  restricted  sense.  It  seems  quite  an 
admissible  hypothesis  that  the  hydro-carbons  and  oxy-hydro- 
carbons  which,  in  traversing  the  system,  are  transformed  by 
communicated  chemical  action,  evolve  during  their  transform- 
ation, not  heat  alone,  but  also  other  kinds  of  force.  It  may  be 
that  as  the  nitrogenous  matter,  while  falling  into  more  stable 
molecular  arrangements,  generates  both  that  molecular  agi- 
tation called  heat,  and  such  other  molecular  movements  as  are 
resolved  into  forces  expended  by  the  organism ;  so,  too,  does 
the  non-nitrogenous  matter.  Or  perhaps  the  concomitants  of 
this  metamorphosis  of  non-nitrogenous  matter,  vary  with  the 
conditions.  Heat  alone  may  result  when  it  is  transformed 
while  in  the  circulating  fluids,  but  partly  heat,  and  partly 
another  force,  when  it  is  transformed  in  some  active  tissue  that 
has  absorbed  it :  just  as  coal,  though  producing  little  else  but 
heat  as  ordinarily  burnt,  has  its  heat  partially  transformed  into 
mechanical  motion  if  burnt  in  a  steam-engine  furnace.  In 
such  case,  the  antithesis  of  Liebig  would  be  reduced  to  this ; 
— that  whereas  nitrogenous  substance  is  tissue-food  both  as 
material  for  building-up  tissue  and  as  material  for  its  function  ; 
non-nitrogenous  substance  is  tissue-food  only  as  material  for 
function. 

There  can  be  no  doubt  that  this  thermal  re-action  which 
chemical  action  from  moment  to  moment  produces  in  the  body, 
is  from  moment  to  moment  an  aid  to  further  chemical 
action.  We  before  saw  (First  Principles,  §  103)  that  a  state 
of  raised  molecular  vibration,  is  favourable  to  those  re-dis- 
tributions of  matter  and  motion  which  constitute  Evolution. 
We  saw  that  in  organisms  distinguished  by  the  amount  and 


46  THE   DATA   OF   BIOLOGY. 

rapidity  of  such  re-distributions,  this  raised  state  of  molecular 
vibration  is  conspicuous.  And  we  here  see  that  this  raised 
state  of  molecular  vibration,  is  itself  a  continuous  consequence 
of  the  continuous  molecular  re-distributions  it  facilitates. 
The  heat  generated  by  each  increment  of  chemical  change, 
makes  possible  the  succeeding  increment  of  chemical  change. 
In  the  body  this  connexion  of  phenomena  is  the  same  as  we 
see  it  to  be  out  of  the  body.  Just  as  in  a  burning  piece  of 
wood,  the  heat  given  out  by  the  portion  actually  combining 
with  oxygen,  raises  the  adjacent  portion  to  a  temperature  at 
which  it  also  can  combine  with  oxygen  ;  so,  in  a  living 
animal,  the  heat  produced  by  oxidation  of  each  portion  of 
tissue,  maintains  the  temperature  at  which  the  unoxidized 
portions  can  be  readily  oxidized. 

§  19.  Among  the  forces  called  forth  from  organisms  by 
re-action  against  the  actions  to  which  they  are  subject,  is 
Light.  Phosphorescence  is  in  some  few  cases  displayed  by 
plants — especially  by  certain  fungi.  Among  animals  it  is 
comparatively  common.  All  know  that  there  are  several 
kinds  of  luminous  insects ;  and  many  are  familiar  with  the 
fact  that  luminosity  is  a  characteristic  of  various  marine 
creatures. 

Most  of  the  evidence  goes  to  show  that  this  evolution  of 
light,  as  well  as  the  evolution  of  heat,  is  consequent  on  oxi- 
dation of  the  tissues.  Light,  like  heat,  is  the  expression  of  a 
raised  state  of  molecular  vibration :  the  diiference  between 
them  being  a  difference  in  the  rates  of  vibration.  Hence  by 
chemical  action  on  substances  contained  in  the  organism,  heat 
or  light  may  be  produced,  according  to  the  character  of  the 
resulting  molecular  vibrations.  The  inference  that 

oxidation  is  the  cause  of  this  luminosity,  does  not,  however, 
rest  only  on  d  priori  grounds.  It  is  supported  by  experi- 
mental evidence.  In  phosphorescent  insects,  the  continuance 
of  the  light  is  found  to  depend  on  the  continuance  of  respira- 
tion ;  and  any  exertion  which  renders  respiration  more  active, 


THE    KE-ACTIONS    OF   ORGANIC    MATTER   ON    FOKCES.  47 

increases  the  brilliancy  of  the  light.  Moreover,  by  separating 
the  luminous  matter,  Prof.  Matteucci  has  shown  that  its 
emission  of  light  is  accompanied  by  absorption  of  oxygen 
and  escape  of  carbonic  acid.  The  phosphorescence 

of  marine  animals  has  been  referred  to  other  causes  than 
oxidation.  In  some  cases,  however,  it  is,  I  think,  explicable, 
without  assuming  any  more  special  agency.  Considering  that 
in  creatures  of  the  genus  Noctiluea,  for  example,  to  which  the 
phosphorescence  most  commonly  seen  on  our  own  coasts  is 
due,  there  is  no  means  of  keeping  up  a  constant  circulation, 
we  may  infer  that  the  movements  of  aerated  fluids  through 
their  tissues,  must  be  greatly  affected  by  impulses  received 
from  without.  Hence  it  may  be  that  the  sparkles  visible  at 
night  when  the  waves  break  gently  on  the  beach,  or  when  an 
oar  is  dipped  into  the  water,  are  called  forth  from  these 
creatures  by  the  concussion,  not  because  of  any  unknown 
influence  it  excites,  but  because,  being  propagated  through 
their  delicate  tissues,  it  produces  a  sudden  movement  of  the 
fluids  and  a  sudden  increase  of  chemical  action.  Neverthe- 
less, in  other  phosphorescent  animals  inhabiting  the  sea,  as 
in  the  Pyrosoma  and  in  certain  Annelida,  light  seems  to  be 
really  produced,  not  by  direct  reaction  on  the  action  of 
oxygen,  but  by  some  indirect  re-action  involving  a  trans- 
formation of  force. 

§  20.  The  re-distributions  of  matter  in  general,  are  accom- 
panied by  electrical  disturbances ;  and  there  is  abundant 
evidence  that  electricity  is  generated  during  those  re-distri- 
butions that  are  ever  taking  place  in  organisms.  Experi- 
ments have  shown  "  that  the  skin  and  most  of  the  internal 
membranes  are  in  opposite  electrical  states ; "  and  also  that 
between  different  internal  organs,  as  the  liver  and  the  stomach, 
there  are  electrical  contrasts — such  contrasts  being  greatest 
where  the  processes  going  on  in  the  compared  parts  are  most 
unlike.  It  has  been  proved  by  M.  du  Bois-Keymond  that 
when  any  point  in  the  longitudinal  section  of  a  muscle  is 


48  THE   DATA   OF   BIOLOGY. 

connected  by  a  conductor  with  any  point  in  its  transverse 
section,  an  electric  current  is  established ;  and  further,  that 
like  results  occur  when  nerves  are  substituted  for  muscles. 
The  special  causes  of  these  phenomena  have  not  yet  been 
determined.  Considering  that  the  electric  contrasts  are  most 
marked  where  active  secretions  are  going  on — considering, 
too,  that  while  they  do  not  exist  between  external  parts 
which  are  similarly  related  to  the  vascular  currents,  they  do 
exist  between  external  parts  which  are  dissimilarly  related 
to  the  vascular  currents — and  considering  also  that  they 
are  extremely  difficult  to  detect  where  there  are  no  appre- 
ciable movements  of  fluids ;  it  may  be  that  they  are  due 
simply  to  the  friction  of  heterogeneous  substances,  which  is 
universally  a  cause  of  electric  disturbance.  But  whatever  be 
the.  interpretation,  the  fact  remains  the  same,  that  there  is 
throughout  the  living  organism,  an  unceasing  production  of 
differences  between  the  electric  states  of  different  parts ;  and 
consequently  an  unceasing  restoration  of  electric  equilibrium 
by  the  establishment  of  currents  among  these  parts. 

Besides  these  general,  and  not  conspicuous,  electrical  phe- 
nomena which  appear  to  be  common  to  all  organisms,  vegetal 
as  well  as  animal,  there  are  certain  special  and  strongly 
marked  ones.  I  refer,  of  course,  to  those  which  have  made 
the  Torpedo  and  the  Gymnotus  objects  of  so  much  interest. 
In  these  creatures  we  have  a  genesis  of  electricity  that  is  not 
incidental  on  the  performance  of  their  different  functions  by 
the  different  organs ;  but  one  which  is  itself  a  function, 
having  an  organ  appropriate  to  it.  The  character  of  this 
organ  in  both  these  fishes,  and  its  largely-developed  con- 
nexions with  the  nervous  centres,  have  raised  the  suspicion, 
which  various  experiments  have  thus  far  justified,  that  in  it 
there  takes  place  a  transformation  of  what  we  call  nerve-force 
into  the  force  known  as  electricity :  this  conclusion  being 
more  especially  supported  by  the  fact,  that  substances,  such  as 
morphia  and  strychnia,  which  are  known  to  be  powerful 


THE    RE-ACTIOXS    OF    ORGANIC    MATTER    ON    FORCES.  4:9 

nervous  stimulants,  greatly  increase  the  violence  and  rapidity 
of  the  electric  discharges. 

But  whether  general  or  special,  and  in  whatever  manner 
produced  these  evolutions  of  electricity  are  among  the 
re-actions  of  organic  matter,  called  forth  by  the  actions  to 
which  it  is  subject.  Though  these  re-actions  are  not  direct, 
but  seem  rather  to  be  remote  consequences  of  those  changes 
wrought  by  external  agencies  on  the  organism,  they  are  yet 
incidents  in  that  general  re-distribution  of  motion,  which 
these  external  agencies  initiate ;  and  as  such  must  here  be 
noticed. 

§  21.  To  these  known  modes  of  motion,  has  next  to  be 
added  an  unknown  one.  Heat,  Light,  and  Electricity  are 
emitted  by  inorganic  matter  when  undergoing  changes,  as 
well  as  by  organic  matter.  But  there  is  a  kind  of  force  mani- 
fested in  some  classes  of  living  bodies,  which  we  cannot 
identify  with  any  of  the  forces  manifested  by  bodies  that  are 
not  alive, — a  force  which  is  thus  unknown,  in  the  sense  that 
it  cannot  be  assimilated  with  any  otherwise-recognized  class. 
I  allude  to  what  is  called  nerve-force. 

This  is  habitually  generated  in  all  animals,  save  the  lowest, 
by  incident  forces  of  every  kind.  The  gentle  and  violent 
mechanical  contacts,  which  in  ourselves  produce  sensations 
of  touch  and  pressure — the  additions  and  abstractions  of  mole- 
cular vibration,  which  in  ourselves  produce  sensations  of 
heat  and  cold ;  produce  in  all  creatures  that  have  nervous 
systems,  certain  nervous  disturbances — disturbances  which, 
as  in  ourselves,  are  either  communicated  to  the  chief  nervous 
centre,  and  there  constitute  consciousness,  or  else  result  in 
merely  physical  processes  that  are  set  going  elsewhere  in  the 
organism.  In  special  parts  distinguished  as  organs  of  sense, 
other  external  actions  bring  about  other  nervous  re-actions ; 
that  show  themselves  either  as  special  sensations,  or  as  ex- 
citements which,  without  the  intermediation  of  consciousness, 


50  THE   DATA   OF   BIOLOGY. 

beget  actions  in  muscles  or  other  organs.  Besides 

neural  discharges  that  follow  the  direct  incidence  of  external 
forces,  there  are  others  ever  being  caused  by  the  incidence  of 
forces  which,  though  originally  external,  have  become  internal 
by  absorption  into  the  organism  of  the  agents  exerting  them. 
For  thus  may  be  classed  those  neural  discharges  that  from 
moment  to  moment  result  from  modifications  of  the  tissues, 
wrought  by  substances  carried  to  them  in  the  blood.  That 
the  unceasing  change  of  matter  which  oxygen  and  other 
agents  produce  throughout  the  system,  is  accompanied  by  a 
genesis  of  nerve-force,  is  shown  by  various  facts ; — by  the  fact 
that  nerve-force  is  no  longer  generated,  if  oxygen  be  with- 
held, or  the  blood  prevented  from  circulating  ;  by  the  fact  that 
when  the  chemical  transformation  is  diminished,  as  during 
sleep  with  its  slow  respiration  and  circulation,  there  is  a 
diminution  in  the  quantity  of  nerve-force  ;  in  the  fact  that  an 
excessive  expenditure  of  nerve-force,  involves  excessive  re- 
spiration and  circulation,  and  excessive  waste  of  tissue.  To 
these  proofs  that  nerve-force  is  evolved  in  greater  or  less  quan- 
tity, according  as  the  conditions  to  rapid  molecular  change 
throughout  the  body,  are  well  or  ill  fulfilled ;  may  be  added 
proofs  that  certain  special  molecular  actions,  are  the  causes 
of  these  special  re-actions.  The  effects  of  alcohol,  ether, 
chloroform,  and  the  vegeto-alkalies,  put  beyond  doubt  the 
inference,  that  the  overthrow  of  molecular  equilibrium  by 
chemical  affinity,  when  it  occurs  at  certain  places  in  the  body, 
results  in  the  overthrow  of  equilibrium  in  the  nerves  pro- 
ceeding from  these  places — results,  that  is,  in  the  propagation 

through  these  nerves,  of  the  change  called  a  nervous  dis- 
cs J  G 

charge.  Indeed,  looked  at  from  this  point  of  view, 

the  two  classes  of  nervous  changes — the  one  initiated  from 
without  and  the  other  from  within — are  seen  to  merge  into 
one  class.  Both  of  them  may  be  traced  to  metamorphosis  of 
tissue.  There  can  be  little  doubt  that  the  sensations  of 
touch  and  pressure,  are  consequent  on  accelerated  changes  of 
matter,  produced  by  mechanical  disturbance  of  the  mingled 


THE    RE-ACTIONS    OF   ORGANIC   MATTER    ON    FORCES.  51 

fluids  and  solids  composing  the  parts  affected.  There  is 
abundant  evidence  that  the  sensation  of  taste,  is  due  to  the 
chemical  actions  set  up  by  particles  which  find  their  way 
through  the  membrane  covering  the  nerves  of  taste  ;  for,  as 
Prof.  Graham  points  out,  sapid  substances  all  belong  to  the 
class  of  crystalloids,  which  are  able  rapidly  to  permeate 
animal  tissue,  while  colloids,  which  cannot  pass  through 
animal  tissue,  are  all  insipid.  Similarly  with  the  sense  of 
smell.  Substances  which  excite  this  sense,  are  necessarily 
more  or  less  volatile ;  and  their  volatility  being  the  result  of 
their  molecular  mobility,  implies  that  they  have  in  a  high 
degree,  the  power  of  getting  at  the  olfactory  nerves  by  pene- 
trating their  mucous  investment.  Again,  the  facts  which 
photography  has  familiarized  us  with,  make  it  clear  that 
those  nervous  impressions  called  colours,  are  primarily  due 
to  certain  changes  wrought  by  light  in  the  substance  of  the 
retina.  And  though,  in  the  case  of  hearing,  we  cannot  so 
clearly  trace  the  connexion  of  cause  and  effect ;  yet  as  we  see 
that  the  auditory  apparatus  is  one  fitted  to  intensify  those 
vibrations  constituting  sound,  and  to  convey  them  to  a  recep- 
tacle containing  fluid  in  which  nerves  are  immersed ;  it  can 
scarcely  be  doubted  that  the  sensation  of  sound  proximately 
results  from  atomic  re-arrangements  caused  in  these  nerves 
by  the  vibrations  of  the  fluid  :  knowing,  as  we  do,  that  the 
re-arrangement  of  atoms  is  in  all  cases  aided  by  agita- 
tion. Perhaps,  however,  the  best  proof  that  nerve- 
force,  whether  peripheral  or  central  in  its  origin,  results  from 
chemical  transformation,  lies  in  the  fact  that  most  of  the 
chemical  agents  which  powerfully  affect  the  nervous  system, 
affect  it  whether  applied  at  the  centre  or  the  periphery.  Vari- 
ous acids,  mineral  and  vegetal,  are  tonics — the  stronger  ones 
being  usually  the  stronger  tonics ;  and  this  which  we  call 
their  acidity,  implies  a  power  in  them  of  acting  on  the  nerves 
of  taste,  while  the  tingling  or  pain  that  follows  their  absorp- 
tion through  the  skin,  implies  that  the  nerves  of  touch  are 
acted  on   by  them.      Similarly  with  certain  vegeto-alkalies 


52  THE   DATA    OF   BIOLOGY. 

which  are  peculiarly  bitter.  These  by  their  bitterness,  show 
that  they  affect  the  extremities  of  the  nerves ;  while  by  their 
tonic  properties,  they  show  that  they  affect  the  nervous 
centres — the  most  intensely  bitter  among  them,  strychnia, 
being  the  most  powerful  nervous  stimulant.  However  true 
it  may  be  that  this  relation  in  not  a  regular  one,  since  opium, 
hashish,  and  some  other  drugs,  which  work  marked  effects  on 
the  brain,  are  not  remarkably  sapid — however  true  it  may  be 
that  there  are  relations  between  particular  substances  and 
particular  parts  of  the  nervous  system ;  yet  such  instances 
do  but  qualify,  without  negativing,  the  general  proposition. 
The  truth  of  this  proposition  can  scarcely  be  doubted  when, 
to  the  evidence  above  given,  is  added  the  fact  that  various 
condiments  and  aromatic  drugs  are  given  as  nervous  stimu- 
lants ;  and  the  fact  that  anaesthetics,  besides  the  general  effects 
they  produce  when  inhaled  or  swallowed,  produce  local  effects 
of  like  kind  when  absorbed  through  the  skin ;  and  the  fact 
that  ammonia,  which  in  consequence  of  its  extreme  molecular 
mobility,  so  quickly  and  so  violently  excites  the  nerves  be- 
neath the  skin,  as  well  as  those  of  the  tongue  and  the  nose, 
is  a  rapidly-acting  stimulant  when  taken  internally. 

Whether  we  shall  ever  know  anything  more  of  this  nerve- 
force,  than  that  it  is  some  species  of  molecular  disturbance 
that  is  propagated  from  end  to  end  of  a  nerve,  it  is  impossi- 
ble to  say.  Whether  a  nerve  is  merely  a  conductor,  which 
delivers  at  one  of  its  extremities  an  impulse  received  at  the 
other ;  or  whether,  as  some  now  think,  it  is  itself  a  generator 
of  force  which  is  initiated  at  one  extremity  and  accumulates 
in  its  course  to  the  other  extremity  ;  are  also  questions  which 
cannot  yet  be  answered.  All  we  know  is,  that  forces  capable 
of  working  molecular  changes  in  nerves,  are  capable  of 
calling  forth  from  them  manifestations  of  activity — dis- 
charges of  some  force,  which,  though  probably  allied  to  elec- 
tricity, is  not  identical  with  it.  And  our  evidence  that  nerve- 
force  is  thus  originated,  consists  not  only  of  such  facts  as  the 
above,  but  also  of  more  conclusive  facts  established  by  direct 


THE    RE-ACTIONS    OF    ORGANIC    MATTER    ON    FORCES.  53 

experiments  on  nerves — experiments  which  show  that  nerve- 
force  is  generated  when  the  cut  end  of  a  nerve  is  either  me- 
chanically irritated,  or  acted  on  by  some  chemical  agent,  or 
subject  to  the  galvanic  current — experiments  which  thus 
prove  that  nerve-force  is  liberated  by  whatever  disturbs  the 
molecular  equilibrium  of  nerve-substance.  And  this  is  all 
which  it  is  necessary  for  us  here  to  understand. 

§  22.  The  most  important  of  these  re-actions  called  forth 
from  organisms  by  surrounding  actions,  remains  to  be  noticed. 
To  the  above  various  forms  of  insensible  motion  thus  caused, 
we  have  to  add  sensible  motion.  On  the  production  of  this 
mode  of  force,  more  especially  depends  the  possibility  of  all 
vital  phenomena.  It  is,  indeed,  usual  to  regard  the  power  of 
generating  sensible  motion,  as  confined  to  one  out  of  the  two 
organic  sub-kingdoms ;  or,  at  any  rate,  as  possessed  by  but 
few  members  of  the  other.  On  looking  closer  into  the  matter, 
however,  we  see  that  plant-life  as  well  as  animal-life,  is  uni- 
versally accompanied  by  certain  manifestations  of  this  power ; 
and  that  plant-life  could  not  otherwise  continue. 

Through  the  humblest,  as  well  as  through  the  highest,  ve- 
getal organisms,  there  are  ever  going  on  certain  re-distribu- 
tions of  matter.  In  protophytes  the  microscope  shows  us  an 
internal  transposition  of  parts,  which  when  not  active  enough 
to  be  immediately  visible,  is  proved  to  exist  by  the  changes 
of  arrangement  that  become  manifest  in  the  course  of  hours 
and  days.  In  the  individual  cells  of  many  higher  plants,  an 
active  movement  among  the  contained  granules  may  be  wit- 
nessed. And  well-developed  cryptogams  in  common  with  all 
phanerogams,  exhibit  this  genesis  of  mechanical  motion  still 
more  conspicuously  in  the  circulation  of  sap.  It  might,  in- 
deed, be  concluded  a  prion,  that  through  plants  displaying 
much  differentiation  of  parts,  an  internal  movement  must  be 
going  on  ;  since,  without  it,  the  mutual  dependence  of  organs 
having  unlike  functions  would  seem  impossible.  Be- 

sides these  motions  of  fluids  kept  up  internally,  plants,  espe- 


54  THE   DATA   OF   BIOLOGY. 

cially  of  the  lower  orders,  are  able  to  move  their  external 
parts  in  relation  to  each  other,  and  also  to  move  about  from 
place  to  place.  Illustrations  in  abundance  will  occur  to  all 
students  of  recent  Natural  History — such  illustrations  as  the 
active  locomotion  of  the  zoospores  of  many  Algee,  the  rhyth- 
mical bendings  of  the  Oscillator  ice,  the  rambling  progression 
of  the  Diatomacem.  In  fact  many  of  these  smallest  vegetals, 
and  many  of  the  larger  ones  in  their  early  stages,  display  a 
mechanical  activity  not  distinguishable  from  that  of  the 
simplest  animals.  Among  well-organized  plants,  which  are 
never  locomotive  in  their  adult  states,  we  still  not  unfre- 
quently  meet  with  relative  motions  of  parts.  To  such  fami- 
liar cases  as  those  of  the  Sensitive  plant  and  the  Venus' 
fly-trap,  many  others  may  be  added.  When  its  base  is 
irritated,  the  stamen  of  the  Berberry  flower  leans  over  and 
touches  the  pistil.  If  the  stamens  of  the  common  wild  Cistus 
be  gently  brushed  with  the  finger,  they  spread  themselves — 
bending  away  from  the  seed-vessel.  And  some  of  the  orchid- 
flowers,  as  Mr.  Darwin  has  recently  shown,  shoot  out  masses 
of  pollen  on  to  the  entering  bee,  when  its  trunk  is  thrust 
down  in  search  of  honey. 

Though  the  power  of  moving  is  not,  as  we  see,  a  character- 
istic of  animals  alone,  yet  in  them,  considered  as  a  class,  it  is 
manifested  to  an  extent  so  marked,  as  practically  to  become 
one  of  their  distinctive  characters — indeed,  we  may  say,  their 
most  distinctive  character.  For  it  is  by  their  immensely 
greater  ability  to  generate  mechanical  motion,  that  animals 
are  enabled  to  perform  those  actions  which  constitute  their 
visible  lives;  and  it  is  by  their  immensely  greater  ability  to 
generate  mechanical  motion,  that  the  higher  orders  of  animals 
are  most  obviously  distinguished  from  the  lower  orders. 
Though,  on  remembering  the  seemingly  active  movements  of 
infusoria,  some  will  perhaps  question  this  last  named  con- 
trast ;  yet,  on  comparing  the  quantities  of  matter  propelled 
through  given  spaces  in  given  times,  they  will  see  that  the 
momentum  evolved  is  far  less  in  the  protozoa  than  in  the 


THE    RE-ACTIONS   OF   ORGANIC   MATTER   ON    FORCES.  55 

teleozoa.  These  sensible  motions  of  animals  are  effected 

by  various  organs  under  various  stimuli.  In  the  humblest 
forms,  and  even  in  some  of  the  more  developed  ones  which 
inhabit  the  water,  locomotion  results  from  the  vibrations  of 
cilia :  the  contractility  resides  in  these  waving  hairs  that 
grow  from  the  surface.  Some  of  the  Acale-phce,  and  their 
allies  the  Polypes,  move  when  mechanically  irritated :  the 
long  pendant  tentacle  of  a  Physalia  is  suddenly  drawn  up  if 
touched  ;  and,  as  well  as  its  tentacles,  the  whole  body  of  a 
Hydra  collapses  if  roughly  handled,  or  jarred  by  some  shock 
in  its  neighbourhood.  In  all  the  higher  animals  however, 
and  to  a  smaller  degree  in  many  of  the  lower,  sensible  mo- 
tion is  generated  by  a  special  tissue,  under  the  special  ex- 
citement of  a  neural  discharge.  Though  it  is  not  strictly  true 
that  such  animals  show  no  sensible  motions  otherwise  caused  ; 
since  all  of  them  have  certain  ciliated  membranes,  and  since 
the  circulation  of  fluid  in  them  is  partially  due  to  osmotic  and 
capillary  actions;  yet,  generally  speaking,  we.  may  say  that 
their  movements  are  effected  only  by  muscles  that  contract 
only  through  the  agency  of  nerves. 

"What  special  transformations  of  force  generate  these  various 
mechanical  changes,  we  do  not,  in  most  cases,  know.  Those 
re-distributions  of  fluid,  with  the  alterations  of  form  sometimes 
caused  by  them,  that  result  from  osmose,  are  not,  indeed, 
quite  incomprehensible.  Certain  motions  of  plants  which, 
like  those  of  the  "  animated  oat,"  follow  contact  with  water, 
are  easily  interpreted  ;  as  are  also  such  other  vegetal  motions 
as  those  of  the  Touch-me-not,  the  Squirting  Cucumber,  and  the 
Carpobolus.  But  we  have  as  yet  no  clue  to  the  mode  in  which 
molecular  movement  is  transformed  into  the  movement  of 
masses,  in  animals.  We  cannot  refer  to  known  causes  the 
rhythmical  action  of  a  Medusa's  disc,  or  that  slow  decrease  of 
bulk  that  spreads  throughout  the  mass  of  an  Alcyonium,  when 
one  of  its  component  individuals  has  been  irritated.  Nor 
are  we  any  better  able  to  say  how  the  insensible  motion 
transmitted  through  a  nerve,  gives  rise  to  sensible  motion  in 


56  THE   DATA    OF   BIOLOGY. 

a  muscle.  It  is  true  that  Science  has  given  to  Art,  several 
methods  of  changing  insensible  into  sensible  motion.  By  ap- 
plying heat  to  water  we  vaporize  it ;  and  the  movement  of  its 
expanding  vapour,  we  transfer  to  solid  matter  ;  but  it  is  clear 
that  the  genesis  of  muscular  movement  is  in  no  way  analogous 
to  this.  The  force  evolved  during  chemical  transformations 
in  a  galvanic  battery,  we  communicate  to  a  soft  iron  magnet 
through  a  wire  coiled  round  it ;  and  it  would  be  quite  possi- 
ble, by  placing  near  to  each  other  several  magnets  thus 
excited,  to  obtain,  through  the  attraction  of  each  for  its 
neighbours,  an  accumulated  movement  made  up  of  their 
separate  movements,  and  thus  to  mechanically  imitate  a  mus- 
cular contraction  ;  but  from  what  we  know  of  organic  mat- 
ter, and  the  structure  of  muscle,  there  is  no  reason  to  suppose 
that  anything  analogous  to  this  takes  place  in  it.  We 

can,  however,  through  one  kind  of  molecular  change,  produce 
sensible  changes  of  aggregation  such  as  possibly  might,  when 
occurring  in  organic  substance,  cause  sensible  motion  in 
it :  I  refer  to  allotropic  change.  Sulphur,  for  example,  as- 
sumes different  crystalline  and  non-crystalline  forms  at  dif- 
ferent temperatures;  and  maybe  made  to  pass  backwards 
and  forwards  from  one  form  to  another,  by  slight  variations 
of  temperature  :  undergoing  each  time  an  alteration  of  bulk. 
We  know  that  this  allotropism,  or  rather  its  analogue  iso- 
merism, prevails  among  colloids — inorganic  and  organic. 
We  also  know  that  some  of  these  metamorphoses  among  col- 
loids, are  accompanied  by  visible  re-arrangements :  instance 
hydrated  silicic  acid,  which,  after  passing  from  its  soluble 
state  to  the  state  of  an  insoluble  jelly,  begins,  in  a  few  days, 
to  contract,  and  to  give  out  part  of  its  contained  water.  Now, 
considering  that  such  isomeric  changes  of  organic  as  well  as 
inorganic  colloids,  are  often  very  rapidly  produced  by  very 
slight  causes,  it  seems  not  impossible  that  some  of  the  colloids 
constituting  muscle,  may  be  thus  changed  by  a  nervous  dis- 
charge— resuming  their  previous  condition  when  the  dis- 
charge  ceases.     And   it  is  conceivable  that  by   structural 


THE    RE- ACTIONS    OF   ORGANIC    MATTER   ON    FORCES.  57 

arrangements,  minute  sensible  motions  so  caused,  may  be  ac- 
cumulated into  large  sensible  motions.  There  is,  however, 
no  evidence  to  support  this  supposition. 

§  23.  But  the  truths  which  it  is  here  our  business  espe- 
cially to  note,  are  quite  independent  of  hypotheses  or  inter- 
pretations. It  is  sufficient  for  the  ends  we  have  in  view,  to 
observe  that  organic  matter  does  exhibit  these  several  conspi- 
cuous re-actions,  when  acted  on  by  incident  forces :  it  is  not 
requisite  that  we  should  know  how  these  re-actions  originate. 

In  the  last  chapter  were  set  forth  the  several  modes  in 
which  incident  forces  cause  re-distributions  of  organic  mat- 
ter ;  and  in  this  chapter  have  been  set  forth  the  several  modes 
in  which  is  manifested  the  motion  accompanying  this  re-dis- 
tribution. There  we  contemplated  under  its  several  aspects, 
the  general  fact,  that  in  consequence  of  its  extreme  instability, 
organic  matter  undergoes  extensive  molecular  re-arrange- 
ments, on  very  slight  changes  of  conditions.  And  here  we 
have  contemplated  under  its  several  aspects,  the  correlative 
general  fact,  that  during  these  extensive  molecular  re-arrange- 
ments, there  are  necessarily  evolved  large  amounts  of  force. 
In  the  one  case  the  atoms  of  which  organic  matter  consists, 
are  regarded  as  changing  from  positions  of  unstable  equi- 
librium to  positions  of  stable  equilibrium  ;  and  in  the  other 
case  they  are  regarded  as  giving  out  in  their  falls  from 
unstable  to  stable  equilibrium,  certain  momenta — momenta 
that  may  be  manifested  as  heat,  light,  electricity,  nerve- 
force  or  mechanical  motion,  according  as  the  conditions 
determine. 

I  will  add  only  that  these  evolutions  of  force  are  rigor- 
ously dependent  on  these  changes  of  matter.  It  is  a  corol- 
lary from  that  primordial  truth  which,  as  we  have  seen, 
underlies  all  other  truths,  {First  Principles,  §§  76,  141,) 
that  whatever  amount  of  power  an  organism  expends  in 
any  shape,  is  the  correlate  and  equivalent  of  a  power  that 
was   taken   into   it   from  without.      On    the    one    hand,  it 


58  THE   DATA   OF   BIOLOGY. 

follows  from  the  persistence  of  force,  that  each  portion  of 
mechanical  or  other  energy  which  an  organism  exerts,  im- 
plies the  transformation  of  as  much  organic  matter  as  con- 
tained this  energy  in  a  latent  state.  And  on  the  other  hand, 
it  follows  from  the  persistence  of  force  that  no  such  trans- 
formation of  organic  matter  containing  this  latent  energy 
can  take  place,  without  the  energy  being  in  one  shape  or 
other  manifested. 


CHAPTER  IV  * 

PROXIMATE  DEFINITION   OF  LIFE. 

§  24.  To  those  who  accept  the  general  doctrine  of  Evolu- 
tion, it  needs  scarcely  to  be  pointed  out  that  classifications  are 
subjective  conceptions,  which  have  no  absolute  demarcations 
in  Nature  corresponding  to  them.  They  are  appliances  by 
which  we  limit  and  arrange  the  matters  under  investigation ; 
and  so  facilitate  our  thinking.  Consequently,  when  we  at- 
tempt to  define  anything  complex,  or  make  a  generalization 
of  facts  other  than  the  most  simple,  we  can  scarcely  ever 
avoid  including  more  than  we  intended,  or  leaving  out  some- 
thing that  should  be  taken  in.  Thus  it  happens  that  on 
seeking  a  definition  of  Life,  we  have  great  difficulty  in  find- 
ing one  that  is  neither  more  nor  less  than  sufficient.  Let 
us  look  at  a  few  of  the  most  tenable  definitions  that  have 
been  given.  While  recognizing  the  inspects  in  which  they 
are  defective,  we  shall  see  what  requirements  a  more  com- 
plete one  must  fulfil. 

*  This  chapter  and  the  following  two  chapters  originally  appeared  in  Part 
III.  of  the  Principles  of  Psychology :  forming  a  preliminary  which,  though  indis- 
pensable to  the  argument  there  developed,  was  somewhat  parenthetical.  Having 
now  to  deal  with  the  general  science  of  Biology  before  the  more  special  one  of 
Psychology,  it  becomes  possible  to  transfer  these  chapters  to  their  proper  place. 
They  have  been  carefully  revised. 

59 


60  THE   DATA   OF   BIOLOGY. 

Schelling  said  that  Life  is  the  tendency  to  individuation. 
This  formula,  until  studied,  conveys  little  meaning.  But  it 
needs  only  to  consider  it  as  illustrated  by  the  facts  of  develop- 
ment, or  by  the  contrasts  between  lower  and  higher  forms  of 
life,  to  recognize  its  value ;  especially  in  respect  of  compre- 
hensiveness. As  before  shown,  however,  {First  Principles, 
§  56),  it  is  objectionable,  partly  on  the  ground  that  it  refers, 
not  so  much  to  the  functional  changes  constituting  Life,  as  to 
the  structural  changes  of  those  aggregations  of  matter  which 
manifest  Life  ;  and  partly  on  the  ground  that  it  includes 
under  the  idea  Life,  much  that  we  usually  exclude  from  it : 
for  instance — crystallization. 

The  definition  of  Richerand, — "  Life  is  a  collection  of 
phenomena  which  succeed  each  other  during  a  limited  time 
in  an  organized  body," — is  liable  to  the  fatal  criticism,  that 
it  equally  applies  to  the  decay  which  goes  on  after  death. 
For  this,  too,  is  "  a  collection  of  phenomena  which  succeed 
each  other  during  a  limited  time  in  an  organized  body." 

"  Life,"  according  to  De  Blainville,  "  is  the  two-fold 
internal  movement  of  composition  and  decomposition,  at  once 
general  and  continuous."  This  conception  is  in  some  re- 
spects too  narrow,  and  in  other  respects  too  wide.  On  the 
one  hand,  while  it  expresses  what  physiologists  distinguish  as 
vegetative  life,  it  excludes  those  nervous  and  muscular 
functions  which  form  the  most  conspicuous  and  distinctive 
classes  of  vital  phenomena.  On  the  other  hand,  it  describes 
not  only  the  integrating  and  disintegrating  processes  going  on 
in  a  living  body,  but  it  equally  well  describes  those  going  on 
in  a  galvanic  battery  ;  which  also  exhibits  a  "  two-fold  in- 
ternal movement  of  composition  and  decomposition,  at  once 
general  and  continuous." 

Elsewhere,  I  have  myself  proposed  to  define  Life  as  "  the 
co-ordination  of  actions ; "  *  and  I  still  incline  towards  this  de- 
finition as  one  answering  to  the  facts  with  tolerable  precision. 

*  See  Westminster  Review  for  April,  1852— Art.  IV.  "A  Theory  of  Popu- 
lation." 


PROXIMATE    DEFINITION   OF    LIFE.  01 

It  includes  all  organic  changes,  alike  of  the  viscera,  the 
limbs,  and  the  brain.  It  excludes  the  great  mass  of  inor- 
ganic changes  ;  which  display  little  or  no  co-ordination.  By 
making  co-ordination  the  specific  characteristic  of  vitality, 
it  involves  the  truths,  that  an  arrest  of  co-ordination  is 
death,  and  that  imperfect  co-ordination  is  disease.  More- 
over, it  harmonizes  with  our  ordinary  ideas  of  life  in  its  dif- 
ferent gradations  :  seeing  that  the  organisms  which  we  rank 
as  low  in  their  degree  of  life,  are  those  which  display  but 
little  co-ordination  of  actions ;  and  seeing  that  from  these  up 
to  man,  the  recognized  increase  in  degree  of  life  corresponds 
with  an  increase  in  the  extent  and  complexity  of  co-ordina- 
tion. But,  like  the  others,  this  definition  includes  too  much  ; 
for  it  may  be  said  of  the  Solar  System,  with  its  regularly- 
recurring  movements  and  its  self-balancing  perturbations, 
that  it,  also,  exhibits  co-ordination  of  actions.  And  how- 
ever plausibly  it  may  be  argued  that,  in  the  abstract,  the 
motions  of  the  planets  and  satellites  are  as  properly  compre- 
hended in  the  idea  of  life,  as  the  changes  going  on  in  a 
motionless,  unsensitive  seed  ;  yet,  it  must  be  admitted  that 
they  are  foreign  to  that  idea  as  commonly  received,  and 
as  here  to  be  formulated. 

It  remains  to  add  the  definition  since  suggested  by  Mr. 
G.  H.  Lewis — "  Life  is  a  series  of  definite  and  successive 
changes,  both  of  structure  and  composition,  which  take  place 
within  an  individual  without  destroying  its  identity."  The 
last  fact  which  this  statement  has  the  merit  of  brino-ins:  into 
view — the  persistence  of  a  living  organism  as  a  whole,  in 
spite  of  the  continuous  removal  and  replacement  of  its  parts 
— is  important.  But  otherwise  it  may  be  argued,  that  since 
changes  of  structure  and  composition,  though  probably  the 
causes  of  muscular  and  nervous  actions,  are  not  the  muscular 
and  nervous  actions  themselves,  the  definition  excludes  the 
more  visible  movements  with  which  our  idea  of  life  is  most 
associated ;  and  further,  that  in  describing  vital  changes  as 
a  series,  it  scarcely  includes  the  fact  that  many  of  them,  as 


G2  THE   DATA   OF   BIOLOGY. 

Nutrition,  Circulation,  Respiration,  and  Secretion,  in  their 
many  subdivisions,  go  on  simultaneously. 

Thus,  however  well  each  of  these  definitions  expresses 
the  phenomena  of  life  under  some  of  its  aspects,  no  one  of 
them  is  more  than  approximately  true.  It  may  turn  out,  that 
to  find  a  formula  which  will  bear  every  test  is  impossible. 
Meanwhile,  it  is  possible  to  frame  a  more  adequate  formula 
than  any  of  the  foregoing.  As  we  shall  presently  find, 
these  all  omit  an  essential  peculiarity  of  vital  changes  in 
general — a  peculiarity  which,  perhaps  more  than  any  other, 
distinguishes  them  from  non-vital  changes.  Before  specify- 
ing this  peculiarity,  however,  it  will  be  well  to  trace  our  way, 
step  by  step,  to  as  complete  an  idea  of  Life  as  may  be  reached 
from  our  present  stand-point :  by  doing  which,  we  shall  both 
see  the  necessity  for  each  limitation  as  it  is  made,  and  ulti- 
mately be  led  to  feel  the  need  for  a  further  limitation. 

And  here,  as  the  best  mode  of  determining  what  are  those 
general  characteristics  which  distinguish  vitality  from  non- 
vitality,  we  shall  do  well  to  compare  the  two  most  unlike 
kinds  of  vitality,  and  see  in  what  they  agree.  Manifestly, 
that  which  is  essential  to  Life  must  be  that  which  is  common 
to  Life  of  all  orders.  And  manifestly,  that  which  is  common 
to  all  forms  of  Life,  will  most  readily  be  seen  on  contrasting 
those  forms  of  Life  which  have  the  least  in  common,  or  are 
the  most  unlike.* 

§  25.  Choosing  assimilation,  then,  for  our  example  of 
bodily  life,  and  reasoning  for  our  example  of  that  life 
known  as  intelligence ;  it  is  first  to  be  observed,  that  they 
are  both  processes  of  change.  Without  change,  food  cannot 
be  taken  into  the  blood  nor  transformed  into  tissue :  without 

*  This  paragraph  replaces  a  sentence  that,  in  The  Principles  of  Psychology, 
referred  to  a  preceding  chapter  on  "  Method  ; "  in  which  the  mode  of  procedure 
here  indicated,  was  set  forth  as  a  mode  to  be  systematically  pursued  in  the  choice 
of  hypotheses.  Should  opportunity  ever  permit,  this  chapter  on  Method  will  be 
embodied,  along  with  other  matter  on  the  same  topic,  in  a  General  Introduction 
to  First  Principles. 


PROXIMATE    DEFINITION    OF   LIFE.  C3 

change,  there  can  be  no  getting  from  premisses  to  conclusion. 
And  it  is  this  conspicuous  manifestation  of  change,  which 
forms  the  substratum  of  our  idea  of  Life  in  general.  Doubt- 
less we  see  innumerable  changes  to  which  no  notion  of  vital- 
ity attaches :  inorganic  bodies  are  ever  undergoing  changes 
of  temperature,  changes  of  colour,  changes  of  aggregation. 
But  it  will  be  admitted  that  the  great  majority  of  the  phe- 
nomena displayed  by  inorganic  bodies,  are  statical  and  not 
dynamical ;  that  the  modifications  of  inorganic  bodies  are 
mostly  slow  and  unobtrusive ;  that  on  the  one  hand,  when 
we  see  sudden  movements  in  inorganic  bodies,  we  are  apt  to 
assume  living  agency,  and  on  the  other  hand,  when  we  see 
no  movements  in  organic  bodies,  we  are  apt  to  assume  death. 
From  all  which  considerations  it  is  manifest,  that  be  the 
requisite  qualifications  what  they  may,  a  definition  of  Life 
must  be  a  definition  of  some  kind  of  change  or  changes. 

On  further  comparing  assimilation  and  reasoning,  with  a 
view  of  seeing  in  what  respect  the  change  displayed  in  both 
differs  from  non-vital  change,  we  find  that  it  differs  in  being 
not  simple  change,  but  change  made  up  of  successive  changes. 
The  transformation  of  food  into  tissue,  involves  mastication, 
deglutition,  chymification,  chylification,  absorption,  and  those 
various  actions  gone  through  after  the  lacteal  ducts  have 
poured  their  contents  into  the  blood.  Carrying  on  an  argu- 
ment necessitates  a  long  chain  of  states  of  consciousness; 
each  implying  a  change  of  the  preceding  state.  Inorganic 
changes,  however,  do  not  in  any  considerable  degree  exhibit 
this  peculiarity.  It  is  true  that  from  meteorologic  causes, 
inanimate  objects  are  daily,  sometimes  hourly,  undergoing 
modifications  of  temperature,  of  bulk,  of  hygrometric  and 
electric  condition.  Not  only,  however,  do  these  modifications 
lack  that  conspicuousness  and  that  rapidity  of  succession 
which  vital  ones  possess,  but  vital  ones  form  an  additional 
series.  Living  as  well  as  not-living  bodies  are  affected 
by  atmospheric  influences ;  and  beyond  the  changes  which 
these  produce,  living  bodies  exhibit  other  changes,  more  nu- 


64  THE   DATA    OF    BIOLOGY. 

merous  and  more  marked.  So  that  though  organic  change 
is  not  rigorously  distinguished  from  inorganic  change  by 
presenting  successive  phases — though  some  inanimate  objects, 
as  watches,  display  phases  of  change  both  quick  and  nu- 
merous— though  all  objects  are  ever  undergoing  change  of 
some  kind,  visible  or  invisible — though  there  is  scarcely  any 
object  which  does  not,  in  the  lapse  of  time,  undergo  a  con- 
siderable amount  of  change  that  is  fairly  divisible  into  phases; 
yet,  vital  change  so  greatly  exceeds  other  change  in  its  dis- 
play of  varying  phases,  that  we  may  consider  this  as  prac- 
tically one  of  its  characteristics.  Life,  then,  as  thus  roughly 
differentiated,  may  be  regarded  as  change  presenting  succes- 
sive phases ;  or  otherwise,  as  a  series  of  changes.  And  it 
should  be  observed,  as  a  fact  in  harmony  with  this  concep- 
tion, that  the  higher  the  life  the  more  conspicuous  the  varia- 
tions. On  comparing  inferior  with  superior  organisms,  these 
last  will  be  seen  to  display  more  rapid  changes,  or  a  more 
lengthened  series  of  them,  or  both. 

Contemplating  afresh  our  two  typical  phenomena,  we 
may  see  that  vital  change  is  further  distinguished  from  non- 
vital  change,  by  being  made  up  of  many  simultaneous  changes. 
Assimilation  is  not  simply  a  series  of  actions,  but  includes 
many  actions  going  on  together.  During  mastication  the 
stomach  is  busy  with  the  food  already  swallowed  ;  on  which 
it  is  both  pouring  out  solvent  fluids  and  expending  muscular 
efforts.  While  the  stomach  is  still  active,  the  intestines  are 
performing  their  secretive,  contractile,  and  absorbent  func- 
tions ;  and  at  the  same  time  that  one  meal  is  being  digested, 
the  nutriment  obtained  from  a  previous  meal  is  undergoing 
that  transformation  into  tissue  which  constitutes  the  final  act 
of  assimilation.  So  also  is  it,  in  a  certain  sense,  with  mental 
changes.  Though  the  states  of  consciousness  which  make  up 
an  argument  occur  in  series,  yet,  as  each  of  these  states  is 
complex — implies  the  simultaneous  excitement  of  those  many 
faculties  by  which  the  perception  of  any  object  or  relation 
has  been  effected ;   it  is  obvious  that  each  such  change  in 


PROXIMATE   DEFINITION   OF    LIFE.  65 

consciousness  implies  manj7  component  changes.  In 

this  respect  too,  however,  it  must  be  admitted  that  the 
distinction  between  animate  and  inanimate  is  not  precise. 
No  mass  of  dead  matter  can  have  its  temperature  altered, 
without  at  the  same  time  undergoing  an  alteration  in  bulk, 
and  sometimes  also  in  hygrometric  state.  An  inorganic 
body  cannot  be  oxidized,  without  being  at  the  same  time 
changed  in  weight,  colour,  atomic  arrangement,  temperature, 
and  electric  condition.  And  in  some  vast  and  mobile  aggre- 
gates like  the  sea,  the  simultaneous  as  well  as  the  successive 
changes  displayed,  outnumber  those  going  on  in  an  animal. 
Nevertheless,  speaking  generally,  a  living  thing  is  distin- 
guished from  a  dead  thing,  by  the  multiplicity  of  the  changes 
at  any  moment  taking  place  in  it.  Add  to  which,  that  by 
this  peculiarity,  as  by  the  previous  one,  not  only  is  the  vital 
more  or  less  clearly  marked  off  from  the  non-vital  ;  but 
creatures  possessing  high  vitality  are  marked  off  from  those 
possessing  low  vitality.  It  needs  but  to  contrast  the  many 
organs  co-operating  in  a  mammal,  with  the  few  in  a  polype, 
to  see  that  the  actions  which  are  progressing  together  in  the 
body  of  the  first,  as  much  exceed  in  number  the  actions  pro- 
gressing together  in  the  body  of  the  last,  as  these  do  those 
in  a  stone.  As  at  present  analyzed,  then,  Life  consists  of 
simultaneous  and  successive  changes. 

Continuing  the  comparison,  we  next  find  that  vital  changes, 
both  visceral  and  cerebral,  differ  from  other  changes  in  their 
heterogeneity.  Neither  the  simultaneous  acts  nor  the  serial 
acts,  which  together  constitute  the  process  of  digestion,  are 
at  all  alike.  The  states  of  consciousness  comprised  in  any 
ratiocination  are  not  repetitions  of  each  other,  either  in  com- 
position or  in  modes  of  dependence.  Inorganic  processes,  on 
the  other  hand,  even  when  like  organic  ones  in  the  number 
of  the  simultaneous  and  successive  changes  they  involve,  are 
unlike  them  in  the  homogeneity  of  these  changes.  In  the 
case  of  the  sea,  just  referred  to,  it  is  observable  that  count- 
less as  are  the  actions  at  any  moment  going  on,  they  are 


G6  the  data  of  biology. 

mostly  mechanical  actions  that  are  to  a  great  degree  similar  ; 
and  in  this  respect  widely  differ  from  the  actions  of  any  mo- 
ment taking  place  in  an  organism  :  which  not  only  belong  to 
the  several  classes,  mechanical,  chemical,  thermal,  electric,  but 
present  under  each  of  these  classes,  innumerable  unlike  actions. 
Even  where  life  is  nearly  simulated,  as  by  the  working  of  a 
steam-engine,  we  may  see  that  considerable  as  is  the  number 
of  simultaneous  changes,  and  rapid  as  are  the  successive  ones, 
the  regularity  with  which  they  soon  recur  in  the  same  order 
and  degree,  renders  them  unlike  those  varied  changes  exhi- 
bited by  a  living  creature.  Still,  it  will  be  found  that 
this  peculiarity,  like  the  foregoing  ones,  does  not  divide  the 
two  classes  of  changes  with  precision  ;  inasmuch  as  there  are 
inanimate  things  which  exhibit  considerable  heterogeneity  of 
change  :  for  instance,  a  cloud.  The  variations  of  state  which 
this  undergoes,  both  simultaneous  and  successive,  are  many 
and  quick  ;  and  they  differ  widely  from  each  other  both  in 
quality  and  quantity.  At  the  same  instant  there  may  occur 
in  a  cloud,  change  of  position,  change  of  form,  change  of 
size,  change  of  density,  change  of  colour,  change  of  tem- 
perature, change  of  electric  state  ;  and  these  several  kinds  of 
change  are  continuously  displayed  in  different  degrees  and 
combinations.  Yet  notwithstanding  this,  when  we  consider 
that  very  few  inorganic  objects  manifest  heterogeneity  of 
change  in  a  marked  manner,  while  all  organic  objects  mani- 
fest it ;  and  further,  that  in  ascending  from  low  to  high  forms 
of  life,  we  meet  with  an  increasing  variety  in  the  kinds  and 
amounts  of  changes  displayed  ;  we  see  that  there  is  here 
a  further  leading  distinction  between  organic  and  inorganic 
actions.  According  to  this  modified  conception,  then,  Life  is 
made  up  of  heterogeneous  changes  both  simultaneous  and 
successive. 

If  now  we  look  for  some  point  of  agreement  between  the 
assimilative  and  logical  processes,  by  which  they  are  distin- 
guished from  those  inorganic  processes  that  are  most  like 
them  in  the  heterogeneity  of  the  simultaneous  and  successive 


PROXIMATE    DEFINITION   OF    LIFE.  67 

changes  they  comprise,  we  discover  that  they  are  distinguish- 
ed by  the  combination  subsisting  among  their  constituent 
changes.  The  acts  that  make  up  digestion  are  mutually  de- 
pendent. Those  composing  a  train  of  reasoning  are  in  close 
connection.  And  generally,  it  is  to  be  remarked  of  vital 
changes,  that  each  is  made  possible  by  all,  and  all  are  affected 
by  each.  Respiration,  circulation,  absorption,  secretion,  in 
their  many  sub-divisions,  are  bound  up  together.  Muscular 
contraction  involves  chemical  change,  change  of  temperature, 
and  change  in  the  excretions.  Active  thought  influences  the 
operations  of  the  stomach,  of  the  heart,  of  the  kidneys.  But  we 
miss  this  union  among  inorganic  processes.  Life-like  as  may 
seem  the  action  of  a  volcano  in  respect  of  the  heterogeneity 
of  its  many  simultaneous  and  successive  changes,  it  is  not  life- 
like in  respect  of  their  combination.  Though  the  chemical, 
mechanical,  thermal,  and  electric  phenomena  exhibited,  have 
some  inter-dependence  ;  yet  the  emission  of  stones,  mud,  lava, 
flame,  ashes,  smoke,  steam,  usually  takes  place  irregularly  in 
quantity,  order,  intervals,  and  mode  of  conjunction.  Even 
here,  however,  it  cannot  be  said  that  inanimate  things  pre- 
sent no  parallels  to  animate  ones.  A  glacier  may  be  instanced 
as  showing  nearly  as  much  combination  in  its  changes  as  a 
plant  of  the  lowest  organization.  It  is  ever  growing  and 
ever  decaying  ;  and  the  rates  of  its  composition  and  decom- 
position preserve  a  tolerably  constant  ratio.  It  moves ;  and 
its  motion  is  in  immediate  dependence  on  its  thawing.  It 
emits  a  torrent  of  water,  which,  in  common  with  its  motion, 
undergoes  annual  variations,  as  plants  do.  During  part 
of  the  year  the  surface  melts  and  freezes  alternately ;  and 
on  these  changes  are  dependent  the  variations  in  movement, 
and  in  efflux  of  water.  Thus  we  have  growth,  decay,  changes 
of  temperature,  changes  of  consistence,  changes  of  velocity, 
changes  of  excretion,  all  going  on  in  connexion  ;  and  it  may 
be  as  truly  said  of  a  glacier  as  of  an  animal,  that  by  cease- 
less integration  and  disintegration  it  gradually  undergoes  an 
entire  change  of  substance  without  losing  its  individuality. 


G8  THE    DATA    OF    BIOLOGY. 

This  exceptional  instance,  however,  will  scarcely  be  held  to 
obscure  that  broad  distinction  from  inorganic  processes, 
which  organic  processes  derive  from  the  combination  among 
their  constituent  changes.  And  the  reality  of  this  distinction 
becomes  yet  more  manifest  when  we  find  that,  in  common 
with  previous  ones,  it  not  only  marks  off  the  living  from  the 
not-living,  but  also  things  which  live  little  from  things  which 
live  much.  For  while  the  changes  going  on  in  a  plant  or  a 
zoophyte  are  so  imperfectly  combined  that  they  can  continue 
after  it  has  been  divided  into  two  or  more  pieces,  the  com- 
bination among  the  changes  going  on  in  a  mammal  is  so 
close  that  no  part  cut  off  from  the  rest  can  live,  and  any  con- 
siderable disturbance  of  one  function  causes  a  cessation  of  the 
others.  Life,  therefore,  as  we  now  regard  it,  is  a  com- 
bination of  heterogeneous  changes,  both  simultaneous  and 
successive. 

Once  more  looking  for  a  characteristic  common  to  these 
two  kinds  of  vital  action,  we  perceive  that  the  combinations 
of  heterogeneous  changes  which  constitute  them,  differ  from 
the  few  combinations  which  they  otherwise  resemble,  in  re- 
spect of  definiteness.  The  associated  changes  going  on  in  a 
glacier,  admit  of  indefinite  variation.  Under  a  conceivable 
alteration  of  climate,  its  thawing  and  its  progression  may  be 
stopped  for  myriads  of  years,  without  disabling  it  from  again 
displaying  these  phenomena  under  appropriate  conditions. 
By  a  geological  convulsion,  its  motion  may  be  arrested  with- 
out an  arrest  of  its  thawing ;  or  by  an  increase  in  the  in- 
clination of  the  surface  it  slides  over,  its  motion  may  be 
accelerated  without  accelerating  its  rate  of  dissolution. 
Other  things  remaining  the  same,  a  more  rapid  deposit  of 
snow  may  cause  an  indefinite  increase  of  bulk  ;  or,  conversely, 
the  accretion  may  entirely  cease,  and  yet  all  the  other  actions 
continue  until  the  mass  disappears.  Here,  then,  the  combina- 
tion has  none  of  that  definiteness  which,  in  a  plant,  marks 
the  mutual  dependence  of  assimilation,  respiration,  and  cir- 
culation ;   much   less   has  it  that   definiteness  seen  in   the 


PROXIMATE    DEFINITION    OF   LIFE.  69 

mutual  dependence  of  the  chief  animal  functions :  no  one  of 
which  can  be  varied  without  varying  the  rest :  no  one  of 
which  can  go  on  unless  the  rest  go  on.  It  is  this  definiteness 
of  combination  which  distinguishes  the  changes  occurring 
in  a  living  body  from  those  occurring  in  a  dead  one.  Decom- 
position exhibits  both  simultaneous  and  successive  changes, 
which  are  to  some  extent  heterogeneous,  and  in  a  sense  com- 
bined ;  but  they  are  not  combined  in  a  definite  manner.  They 
vary  according  as  the  surrounding  medium  is  air,  water,  or 
earth.  They  alter  in  nature  with  the  temperature.  If  the  local 
conditions  are  unlike,  they  progress  differently  in  different 
parts  of  the  mass,  without  mutual  influence.  They  may  end  in 
producing  gases,  or  adipocire,  or  the  dry  substance  of  which 
mummies  consist.  They  may  occupy  a  few  days,  or  thousands 
of  years.  Thus,  neither  in  their  simultaneous  nor  in  their  suc- 
cessive changes,  do  dead  bodies  display  that  definiteness  of 
combination  which  characterizes  living  ones.  It  is 

true  that  in  some  inferior  creatures  the  cycle  of  successive 
changes  admits  of  a  certain  indefiniteness — that  it  may 
be  apparently  suspended  for  a  long  period  by  desiccation  or 
freezing  ;  and  may  afterwards  go  on  as  though  there  had 
been  no  breach  in  its  continuity.  But  the  circumstance 
that  only  a  low  order  of  life  permits  the  cycle  of  its  changes 
to  be  thus  modified,  serves  but  to  suggest  that,  like  the  pre- 
vious characteristics,  this  characteristic  of  definiteness  in  its 
combined  changes,  distinguishes  high  vitality  from  low  vital- 
ity, as  it  distinguishes  low  vitality  from  inorganic  processes. 
Hence,  our  formula  as  further  amended  reads  thus : — Life  is 
a  definite  combination  of  heterogeneous  changes,  both  simul- 
taneous and  successive. 

Finally,  we  shall  still  better  express  the  facts,  if,  instead  of 
saying  a  definite  combination  of  heterogeneous  changes,  we 
say  the  definite  combination  of  heterogeneous  changes.  As 
it  at  present  stands,  the  definition  is  defective  both  in  allow- 
ing that  there  may  be  other  definite  combinations  of  hetero- 
geneous changes,  and  in  directing  attention  to  the  hetero- 


70  THE   DATA   OF   BIOLOGY. 

geneous  changes  rather  than  to  the  definiteness  of  their 
combination.  Just  as  it  is  not  so  much  its  chemical  elements 
which  constitute  an  organism,  as  it  is  the  arrangement  of 
them  into  special  tissues  and  organs ;  so  it  is  not  so  much  its 
heterogeneous  changes  which  constitute  Life,  as  it  is  the  de- 
finite combination  of  them.  Observe  what  it  is  that  ceases 
when  life  ceases.  In  a  dead  body  there  are  going  on  hetero- 
geneous changes,  both  simultaneous  and  successive.  What 
then  has  disappeared  ?  The  definite  combination  has  dis- 
appeared. Mark,  too,  that  however  heterogeneous  the  simul- 
taneous and  successive  changes  exhibited  by  an  inorganic 
object,  as  a  volcano,  we  much  less  tend  to  think  of  it  as 
living,  than  we  do  a  watch  or  a  steam-engine,  which,  though 
displaying  homogeneous  changes,  displays  them  definitely 
combined.  So  dominant  an  element  is  this  in  our  idea  of 
Life,  that  even  when  an  object  is  motionless,  yet,  if  its  parts 
be  definitely  combined,  we  conclude  either  that  it  has  had 
life,  or  has  been  made  by  something  having  life.  Thus  then, 
we  conclude  that  Life  is — the  definite  combination  of  hetero- 
geneous changes,  both  simultaneous  and  successive. 

§  26.  Such  is  the  conception  at  which  we  arrive  without 
changing  our  stand-point.  It  is,  however,  an  incomplete 
conception.  This  ultimate  formula  (which  is  to  a  consider- 
able extent  identical. with  one  above  given — "the  co-ordina- 
tion of  actions ; "  seeing  that  "  definite  combination "  is 
synonymous  with  "  co-ordination,"  and  "  changes  both  si- 
multaneous and  successive"  are  comprehended  under  the 
term  "  actions  ; ''  but  which  differs  from  it  in  specifying  the 
fact,  that  the  actions  or  changes  are  "  heterogeneous  ") — this 
ultimate  formula,  I  say,  is  after  all  but  proximately  correct. 
It  is  true  that  it  does  not  fail  by  including  the  growth  of 
a  crystal ;  for  the  successive  changes  this  implies  cannot  be 
called  heterogeneous.  It  is  true  that  the  action  of  a  galvanic 
battery  is  not  comprised  in  it ;  since  here,  too,  heterogeneity 
is  not  exhibited  by  the  successive  changes.     It  is  true  that  by 


PROXIMATE   DEFINITION    OF    LIFE.  71 

tins  same  qualification  the  motions  of  the  Solar  System  are 
excluded ;  as  are  also  those  of  a  watch  and  a  steam-engine. 
It  is  true,  moreover,  that  while,  in  virtue  of  their  heteroge- 
neity, the  actions  going  on  in  a  cloud,  in  a  volcano,  in  a 
glacier,  fulfil  the  definition ;  they  fall  short  of  it  in  lacking 
definiteness  of  combination.  It  is  further  true  that  this 
definiteness  of  combination,  distinguishes  the  changes  taking 
place  in  an  organism  during  life,  from  those  which  commence 
at  death.  And  beyond  all  this  it  is  true  that,  as  well  as 
serving  to  mark  off,  more  or  less  clearly,  organic  actions  from 
inorganic  actions,  each  member  of  the  definition  serves  to 
mark  off  the  actions  constituting  high  vitality  from  those 
constituting  low  vitality ;  seeing  that  life  is  high  in  propor- 
tion to  the  number  of  successive  changes  occurring  between 
birth  and  death  ;  in  proportion  to  the  number  of  simultaneous 
changes  ;  in  proportion  to  the  heterogeneity  of  the  changes  ; 
in  proportion  to  the  combination  subsisting  among  the 
changes ;  and  in  proportion  to  the  definiteness  of  their  com- 
bination. Nevertheless,  answering  though  it  does  to  so 
many  requirements,  this  definition  is  essentially  defective. 
It  does  not  convey  a  complete  idea  of  the  thing  contem- 
plated. The  definite  combination  of  heterogeneous  changes, 
both  simultaneous  and  successive,  is  a  formula  which  fails  to 
call  up  an  adequate  conception.  And  it  fails  from  omitting 
the  most  distinctive  peculiarity — the  peculiarity  of  which  we 
have  the  most  familiar  experience,  and  with  which  our  notion 
of  Life  is,  more  than  with  any  other,  associated.  It  remains 
now  to  supplement  the  definition  by  the  addition  of  this 
peculiarity. 


CHAPTER  V. 

THE  CORRESPONDENCE  BETWEEN  LIFE  AND   ITS 
CIRCUMSTANCES. 

§  27.  We  habitually  distinguish  between  a  live  object 
and  a  dead  one,  by  observing  whether  a  change  which  we 
make  in  the  surrounding  conditions,  or  one  which  Nature 
makes  in  them,  is  or  is  not  followed  by  some  perceptible  change 
in  the  object.  By  discovering  that  certain  things  shrink  when 
touched,  or  fly  away  when  approached,  or  start  when  a  noise 
is  made,  the  child  first  roughly  discriminates  between  the 
living  and  the  not  living ;  and  the  man  when  in  doubt 
whether  an  animal  he  is  looking  at  is  dead  or  not,  stirs  it 
with  his  stick ;  or  if  it  be  at  a  distance,  shouts,  or  throws  a 
stone  at  it.  Vegetal  and  animal  life  are  alike  primarily 
recognized  by  this  process.  The  tree  that  puts  ont  leaves 
when  the  spring  brings  a  change  of  temperature,  the  flower 
which  opens  and  closes  with  the  rising  and  setting  of  the 
sun,  the  plant  that  droops  when  the  soil  is  dry,  and  re-erects 
itself  when  watered,  are  considered  alive  because  of  these  in- 
duced changes  ;  in  common  with  the  zoophyte  which  contracts 
on  the  passing  of  a  cloud  over  the  sun,  the  worm  that  comes  to 
the  surface  when  the  ground  is  continuously  shaken,  and  the 
hedgehog  that  rolls  itself  up  when  attacked. 

Not  only,  however,  do  we  habitually  look  for  some  response 
when  an  external  stimulus  is  applied  to  a  living  organism, 
but  we  perceive  a  fitness  in  the  response.  Dead  as  well  as 
living  things  display  changes  under  certain  changes  of  COn- 
72 


CORRESPONDENCE  BETWEEN  LIFE  AND  ITS  CIRCUMSTANCES.    73 

dition  :  instance,  a.  lump  of  carbonate  of  soda  that  effervesces 
when  dropped  into  sulphuric  acid  ;  a  cord  that  contracts 
when  wetted  ;  a  piece  of  bread  that  turns  brown  when  held 
near  the  fire.  But  in  these  cases,  we  do  not  see  a  connexion 
between  the  changes  undergone,  and  the  preservation  of  the 
things  that  undergo  them  ;  or,  to  avoid  any  teleological  im- 
plication— the  changes  have  no  apparent  relations  to  future 
external  events  which  are  sure  or  likely  to  take  place.  In 
vital  changes,  however,  such  relations  are  manifest.  Light 
being  necessary  to  vegetal  life,  we  see  in  the  action  of  a 
plant  which,  when  much  shaded,  grows  towards  the  unshaded 
side,  an  appropriateness  which  we  should  not  see  did  it  grow 
otherwise.  Evidently  the  proceeding  of  a  spider,  which 
rushes  out  when  its  web  is  gently  shaken  and  stays  within 
when  the  shaking  is  violent,  conduce  better  to  the  obtainment 
of  food  and  the  avoidance  of  danger  than  were  the}'  reversed. 
The  fact  that  we  feel  surprise  when,  as  in  the  case  of  a  bird  fas- 
cinated by  a  snake,  the  conduct  tends  towards  self-destruction, 
at  once  shows  how  generally  we  have  observed  an  adaptation 
of  living  changes  to  changes  in  surrounding  circumstances. 

Note  further  the  kindred  truth,  rendered  so  familiar  by 
infinite  repetition  that  we  forget  its  significance,  that  there 
is  invariably,  and  necessarily,  a  conformity  between  the  vital 
functions  of  any  organism,  and  the  conditions  in  which  it  is 
placed — between  the  processes  going  on  inside  of  it,  and  the 
processes  going  on  outside  of  it.  We  know  that  a  fish  can- 
not live  in  air,  or  a  man  in  water.  An  oak  growing  in  the 
ocean,  and  a  seaweed  on  the  top  of  a  hill,  are  incredible 
combinations  of  ideas.  We  find  that  every  animal  is  limited 
to  a  certain  range  of  climate  ;  every  plant  to  certain  zones  of 
latitude  and  elevation.  Of  the  marine  flora  and  fauna,  each 
species  is  found  exclusively  between  such  and  such  depths. 
Some  blind  creatures  flourish  only  in  dark  caves  ;  the  limpet 
only  where  it  is  alternately  covered  and  uncovered  by  the 
tide  ;  the  red-snow  alga  rarely  elsewhere  than  in  the  arctic 
regions  or  among  alpine  peaks. 
6 


74  THE   DATA   OF   BIOLOGY. 

Grouping  together  the  cases  first  named,  in  which  a  parti- 
cular change  in  the  circumstances  of  an  organism  is  followed 
by  a  particular  change  in  it,  and  the  cases  last  named,  in 
which  the  constant  actions  occurring  within  an  organism  im- 
ply some  constant  actions  occurring  without  it ;  we  see  that 
in  both,  the  changes  or  processes  displayed  by  a  living  body 
are  specially  related  to  the  changes  or  processes  in  its  en- 
vironment. And  here  we  have  the  needful  supplement  to 
our  conception  of  Life.  Adding  this  all-important  charac- 
teristic, our  conception  of  Life  becomes — The  definite  com- 
bination of  heterogeneous  changes,  both  simultaneous  and 
successive,  in  corresj)ondence  with  external  co-existences  and 
sequences.  That  the  full  significance  of  this  addition  may  be 
seen,  it  will  be  necessary  to  glance  at  the  correspondence 
under  some  of  its  leading  aspects.* 

§  28.  Neglecting  minor  requirements,  the  actions  going 

*  Speaking  of  "  the  general  idea  of  Kfe,n  M.  Comte  says  :  "  Cette  idee  sup- 
pose, en  effet,  non-seulcment  celle  d'un  etre  organise  de  maniere  a  comporter 
l'etat  vital,  mais  aussi  celle,  non  moins  indispensable,  d'un  certain  ensemble 
d'influences  exterieure  propres  a  son  accomplissement.  Une  telle  harmonie  entre 
l'etre  vivant  et  le  milieu  correspondant,  caracterise  evidemment  la  condition  fon- 
damentale  de  la  vie."  Commenting  on  de  Blainvillc's  definition  of  life,  which  he 
adopts,  he  says  : — "  Cette  lumineuse  definition  ne  me  parait  laisser  rien  d'impor- 
tant  a  desirer,  si  ce  n'est  une  indication  plusdirecte  et  plus  explicitedecesdeux 
conditions  fondamentales  co-relatives,  necessairement  inseparables  de  l'etat  vivant, 
un  organisme  determine  et  un  milieu  convenable."  It  is  strange  that  M.  Comte 
should  have  thus  recognized  the  necessity  of  a  harmony  between  an  organism  and 
its  environment,  as  a  condition  essential  to  life,  and  should  not  have  seen  that  the 
continuous  maintenance  of  such  inner  actions  as  will  counterbalance  outer  actions, 
constitutes  life.  It  is  the  more  strange  that  he  should  have  been  so  near  this 
truth  and  yet  missed  it,  since,  besides  his  wide  range  of  thought,  M.  Comte  is 
often  remarkable  for  his  clear  intuitions.  Lest  by  saying  this,  I  should  deepen  a 
misconception  into  which  some  have  fallen,  let  me  take  the  opportunity  of  stating, 
that  though  I  believe  some  of  M.  Comte's  minor  generalizations  to  be  true  and 
though  I  recognize  the  profundity  of  many  incidental  observations  he  makes,  I 
by  no  means  accept  his  system.  Those  general  doctrines  in  which  I  agree  with 
him,  are  those  which  he  holds  in  common  with  sundry  other  thinkers.  With  all 
those  general  doctrines  which  are  distinctive  of  his  philosophy,  I  disagree — with 
all  those  at  least  that  I  have  definite  knowledge  of ;  for  beyond  the  first  half  of 
his  "  Course  of  Positive  Philosophy,"  I  know  his  opinions  only  by  hearsay. 


CORRESPONDENCE  BETWEEN  LIFE  AND  ITS  CIRCUMSTANCES.    75 

on  in  a  plant  pre-suppose  a  surrounding  medium  containing 
at  least  carbonic  acid  and  water,  together  with  a  due  supply 
of  light  and  a  certain  temperature.  Within  the  leaves 
carbon  is  being  assimilated  and  oxygen  given  off ;  without 
them,  is  the  gas  from  which  the  carbon  is  abstracted,  and  the 
imponderable  agents  that  aid  the  abstraction.  Be  the  nature 
of  the  process  what  it  may,  it  is  clear  that  there  are  external 
elements  prone  to  undergo  special  re-arrangements  under 
special  conditions.  It  is  clear  that  the  plant  in  sunshine 
presents  these  conditions  and  so  effects  these  re-arrange- 
ments. And  thus  it  is  clear  that  the  changes  which  consti- 
tute the  plant's  life,  are  in  correspondence  with  co-existences 
in  its  environment. 

If,  again,  we  ask  respecting  the  lowest  protozoon,  how 
it  lives ;  the  answer  is,  that  while  on  the  one  hand  its  sub- 
stance is  ever  undergoing  oxidation,  it  is  on  the  other  hand 
ever  absorbing  nutriment ;  and  that  it  may  continue  to  exist, 
the  assimilation  must  keep  pace  with,  or  exceed,  the  oxidation. 
If  further  we  ask  under  what  circumstances  these  combined 
changes  are  possible  ;  there  is  the  obvious  reply,  that  the 
medium  in  which  the  protozoon  is  placed,  must  contain  oxy- 
gen and  food — oxygen  in  such  quantity  as  to  produce  some 
disintegration ;  food  in  such  quantity  as  to  permit  that  dis- 
integration to  be  made  good.  In  other  words — the  two 
antagonistic  processes  taking  place  internally,  imply  the  pres- 
ence externally  of  materials  having  affinities  that  can  give 
rise  to  these  processes. 

Leaving  those  lowest  animal  forms  revealed  by  the  mi- 
croscope, which  simply  take  in  through  their  surfaces  the 
nutriment  and  oxygenated  fluids  coming  in  contact  with 
them,  we  pass  to  those  somewhat  higher  forms  which  have 
their  tissues  partially  specialized  into  assimilative  and  re- 
spiratory. In  these  we  see  a  correspondence  between  certain 
actions  in  the  digestive  sac,  and  the  properties  of  certain  sur- 
rounding bodies.  That  a  creature  of  this  order  may  continue 
to  live,  it  is  necessary  not  only  that  there  be  masses  of  sub- 


76  THE   DATA   OF    BIOLOGY. 

stance  in  the  environment  capable  of  transformation  into  its 
own  tissue  ;  but  that  the  introduction  of  these  masses  into  its 
stomach,  shall  be  followed  by  the  secretion  of  a  solvent  fluid 
that  will  reduce  them  to  a  fit  state  for  absorption.  Special 
outer  properties  must  be  met  by  special  inner  properties. 

When,  from  the  process  by  which  food  is  digested,  we 
turn  to  the  processes  by  which  it  is  seized,  we  perceive  the 
same  general  truth.  The  stinging  and  contractile  power  of 
a  polype's  tentacle,  correspond  to  the  sensitiveness  and 
strength  of  the  creatures  serving  it  for  prey.  Unless  that 
external  change  which  brings  one  of  these  creatures  in  con- 
tact with  the  tentacle,  were  quickly  followed  by  those  inter- 
nal changes  which  result  in  the  coiling  and  drawing  up  of 
the  tentacle,  the  polype  would  die  of  inanition.  The  funda- 
mental processes  of  integration  and  disintegration  within  it, 
would  get  out  of  correspondence  with  the  agencies  and  pro- 
cesses without  it ;  and  the  life  would  cease. 

Similarly,  it  may  be  shown  that  when  the  creature  be- 
comes so  large  that  its  tissue  cannot  be  efficiently  supplied 
with  nutriment  by  mere  absorption  through  its  limiting 
membranes,  or  duly  oxygenated  by  contact  with  the  fluid 
that  bathes  its  surface,  there  arises  a  necessity  for  a  circu- 
latory system  by  which  nutriment  and  oxygen  may  be  dis- 
tributed throughout  the  mass  ;  and  the  functions  of  this  sys- 
tem, being  subsidiary  to  the  two  primary  functions,  form 
links  in  the  correspondence  between  internal  and  external 
actions.  The  like  is  obviously  true  of  all  those  subordinate 
functions,  secretory  and  excretory,  that  facilitate  oxidation 
and  assimilation — functions  in  which  we  may  trace,  both  co- 
temporaneous  changes  answering  to  co-existences  in  the  en- 
vironment, and  successive  changes  answering  to  those  changes 
of  composition,  of  temperature,  of  light,  of  moisture,  of  pres- 
sure, which  the  environment  undergoes. 

Ascending  from  the  visceral  actions  to  the  muscular  and 
nervous  actions,  we  find  the  correspondence  displayed  in  a 
manner  still  more  obvious.     Every  act  of  locomotion  implies 


CORRESPONDENCE  BETWEEN  LIFE  AND  ITS  CIRCUMSTANCES.    77 

the  expenditure  of  certain  internal  mechanical  forces,  adapted 
in  amounts  and  directions  to  balance  or  out-balance  certain 
external  ones.  The  recognition  of  an  object  is  impossible 
without  a  harmony  between  the  changes  constituting  per- 
ception, and  particular  properties  co-existing  in  the  environ- 
ment. Escape  from  enemies  supposes  motions  within  the 
organism,  related  in  kind  and  rapidity  to  motions  without  it. 
Destruction  of  prey  requires  a  particular  combination  of  sub- 
jective actions,  fitted  in  degree  and  succession  to  overcome  a 
group  of  objective  ones.  And  so  with  those  countless  auto- 
matic processes  exemplified  in  works  on  animal  instinct. 

In  the  highest  order  of  vital  changes,  the  same  fact  is 
equally  manifest.  The  empirical  generalization  that  guides 
the  farmer  in  his  rotation  of  crops,  serves  to  bring  his  actions 
into  concord  with  certain  of  the  actions  going  on  in  plants 
and  soil.  The  rational  deductions  of  the  educated  navigator 
who  calculates  his  position  at  sea,  constitute  a  series  of  mental 
acts  by  which  his  proceedings  are  conformed  to  surrounding 
circumstances.  Alike  in  the  simplest  inferences  of  the  child, 
and  the  most  complex  ones  of  the  man  of  science,  we  find  a 
correspondence  between  simultaneous  and  successive  changes 
in  the  organism,  and  co-existences  and  sequences  in  its  envi- 
ronment. 

§  29.  This  general  formula,  which  thus  includes  the  lowest 
vegetal  processes  as  well  as  the  highest  manifestations  of  hu- 
man intelligence,  will  perhaps  call  forth  some  criticisms  which 
it  is  desirable  here  to  meet. 

It  may  be  thought  that  there  are  still  a  few  inorganic  ac- 
tions included  in  the  definition  ;  as  for  example  that  displayed 
oy  the  mis-named  storm-glass.  The  feathery  crystallization 
which,  on  a  certain  change  of  temperature,  takes  place  in  the 
solution  contained  by  this  instrument,  and  which  afterwards 
dissolves  to  reappear  in  new  forms  under  new  conditions,  may 
be  held  to  present  simultaneous  and  successive  changes  that 
are  to  some  extent  heterogeneous,  that  occur  with  some  de- 


T8  THE   DATA    OF    BIOLOGY. 

finiteness  of  combination,  and.  above  all,  occur  in  correspond- 
ence with  external  changes.  In  this  case  vegetal  life  is  sim- 
ulated to  a  considerable  extent ;  but  it  is  merely  simulated. 
The  relation  between  the  phenomena  occurring  in  the  storm- 
glass  and  in  the  atmosphere  respectively,  is  really  not  a  cor- 
respondence at  all,  in  the  proper  sense  of  the  word.  Outside 
there  is  a  certain  change  ;  inside  there  is  a  change  of  atomic 
arrangement.  Outside  there  is  another  certain  change ;  in- 
side there  is  another  change  of  atomic  arrangement.  But 
subtle  as  is  the  dependence  of  each  internal  upon  each  ex- 
ternal change,  the  connexion  between  them  does  not,  in  the 
abstract,  differ  from  the  connexion  between  the  motion  of  a 
straw  and  the  motion  of  the  wind  that  disturbs  it.  In  either 
case  a  change  produces  a  change,  and  there  it  ends.  The 
alteration  wrought  by  some  environing  agency  on  an  inani- 
mate object,  does  not  tend  to  induce  in  it  a  secondary  altera- 
tion, that  anticipates  some  secondary  alteration  in  the  en- 
vironment. But  in  every  living  body  there  is  a  tendency 
towards  secondary  alterations  of  this  nature ;  and  it  is  in 
their  production  that  the  correspondence  consists.  The  dif- 
ference may  be  best  expressed  by  symbols.  Let  A  be  a 
change  in  the  environment ;  and  B  some  resulting  change 
in  an  inorganic  mass.  Then  A  having  produced  B,  the  ac- 
tion ceases.  Though  the  change  A  in  the  environment,  is 
followed  by  some  consequent  change  a  in  it ;  no  parallel  se- 
quence in  the  inorganic  mass  simultaneously  generates  in  it 
some  change  b  that  has  reference  to  the  change  a.  Bnt  if  we 
take  a  living  body  of  the  requisite  organization,  and  let  the 
change  A  impress  on  it  some  change  C ;  then,  while  in  the 
environment  A  is  occasioning  a,  in  the  living  body  C  will 
be  occasioning  c :  of  which  a  and  c  will  show  a  certain  con- 
cord in  time,  place,  or  intensity.  And  while  it  is  in  the  con- 
tinuous production  of  such  concords  or  correspondences  that 
Life  consists,  it  is  by  the  continuous  production  of  them  that 
Life  is  maintained. 

The  further  criticism  that  may  be  expected,  concerns  cer- 


CORRESPONDENCE  BETWEEN  LIFE  AND  ITS  CIRCUMSTANCES.    79 

tain  verbal  imperfections  in  the  definition,  which  it  seems 
impossible  to  avoid.  It  may  be  fairly  urged  that  the  word 
correspondence  will  not  include,  without  straining,  the  various 
relations  to  be  expressed  by  it.  It  may  be  asked  : — How  can 
the  continuous  processes  of  assimilation  and  respiration,  cor- 
respond with  the  co-existence  of  food  and  oxygen  in  the  en- 
vironment ?  or  again  : — How  can  the  act  of  secreting  some 
defensive  fluid,  correspond  with  some  external  danger  which 
may  never  occur  ?  or  again  : — How  can  the  dynamical  phe- 
nomena constituting  perception,  correspond  with  the  statical 
phenomena  of  the  solid  body  perceived  ?  The  only  reply  to 
these  questions,  is,  that  we  have  no  word  sufficiently  general 
to  comprehend  all  forms  of  this  relation  between  the  organ- 
ism and  its  medium,  and  yet  sufficiently  specific  to  convey  an 
adequate  idea  of  the  relation  ;  and  that  the  word  correspond- 
ence seems  the  least  objectionable.  The  fact  to  be  expressed 
in  all  cases,  is,  that  certain  changes,  continuous  or  discon- 
tinuous, in  the  organism,  are  connected  after  such  a  manner 
that,  in  their  amounts,  or  variations,  or  periods  of  occurrence, 
or  modes  of  succession,  they  have  a  reference  to  external  ac- 
tions, constant  or  serial,  actual  or  potential — a  reference  such 
that  a  definite  relation  among  any  members  of  the  one  group, 
implies  a  definite  relation  among  certain  members  of  the 
other  group  ;  and  the  word  correspondence  appears  the  best 
fitted  to  express  this  fact. 

§  30.  The  presentation  of  the  phenomena  under  this  gen- 
eral form,  suggests  how  our  definition  of  Life  may  be  reduced 
to  its  most  abstract  shape  ;  and  perhaps  its  best  shape.  By 
regarding  the  respective  elements  of  the  definition  as  relations ; 
we  avoid  both  the  circumlocution  and  the  verbal  inaccuracy ; 
and  that  we  may  so  regard  them  with  propriety  is  obvious. 
If  a  creature's  rate  of  assimilation  is  increased  in  consequence 
of  a  decrease  of  temperature  in  the  environment ;  it  is  that 
the  relation  between  the  food  consumed  and  heat  produced,  is 
so  re-adjusted  by  multiplying   both  its  members,  that  the 


80  THE    DATA    OF    BIOLOGY. 

altered  relation  in  the  surrounding  medium  between  the 
quantity  of  heat  absorbed  from,  and  radiated  to,  bodies  of  a 
given  temperature,  is  counterbalanced.  If  a  sound  or  a  scent 
wafted  to  it  on  the  breeze,  prompts  the  stag  to  dart  away 
from  the  deer-stalker ;  it  is  that  there  exists  in  its  neighbour- 
hood a  relation  between  a  certain  sensible  property  and  cer- 
tain actions  dangerous  to  the  stag,  while  in  its  organism 
there  exists  an  adapted  relation  between  the  impression  this 
sensible  property  produces,  and  the  actions  by  which  danger 
is  escaped.  If  inquiry  has  led  the  chemist  to  a  law  enabling 
him  to  tell  how  much  of  any  one  element  will  combine  with 
so  much  of  another ;  it  is  that  there  has  been  established 
in  him  specific  mental  relations,  which  accord  with  specific 
chemical  relations  in  the  things  around.  Seeing,  then,  that  in 
all  cases  we  may  consider  the  external  phenomena  as  simply 
in  relation,  and  the  internal  phenomena  also  as  simply  in  re- 
lation ;  the  broadest  and  most  complete  definition  of  Life  will 
be — The  continuous  adjustment  of  internal  relations  to  ex- 
ternal relations* 

While  it  is  simpler,  this  modified  formula  has  the  further 
advantage  of  being  somewhat  more  comprehensive.  To  say 
that  it  includes  not  only  those  definite  combinations  of  simul- 
taneous and  successive  changes  in  an  organism,  which  cor- 
respond to  co-existences  and  sequences  in  the  environment, 
but  also  those  structural  arrangements  which  enable  the  or- 
ganism to  adapt  its  actions  to  actions  in  the  environment, 
may  perhaps  be  going  too  far;  for  though  these  structural 
arrangements  present  internal  relations  adjusted  to  external 
relations,  yet  the  continuous  adjustment  of  relations  can 
scarcely  be  held  to  include  ajixed  adjustment  already  made. 
Clearly,  Life,  which  is  made  up  of  dynamiccd  phenomena, 
cannot  be  defined  in  terms  that  shall  at  the  same  time  define 
the  apparatus  manifesting  it,  which  presents  only  statical 
phenomena.  But  wmile  this  antithesis  serves  to  remind  us 
that  the  fundamental  distinction  between  the  organism  and 

*  In  further  elucidation  of  this  general  doctrine,  see  First  Principles,  §  25. 


n 


CORRESPONDENCE  BETWEEN  LIFE  AND  ITS  CIRCUMSTANCES.    81 

its  actions,  is  as  wide  as  that  between  Matter  and  Motion,  it 
at  the  same  time  draws  attention  to  the  fact,  that  if  the 
structural  arrangements  of  the  adult  are  not  properly  in- 
cluded in  the  definition,  yet  the  developmental  processes  by 
which  those  arrangements  were  established,  are  included 
For  that  process  of  evolution  during  which  the  organs  of  the 
embryo  are  fitted  to  their  prospective  functions,  is  from  be 
ginning  to  end  the  gradual  or  continuous  adjustment  of  in 
ternal  relations  to  external  relations.  Moreover,  those  struc- 
tural modifications  of  the  adult  organism,  which,  under  change 
of  climate,  change  of  occupation,  change  of  food,  slowly  bring 
about  some  re-arrangement  in  the  organic  balance,  must  simi- 
larly be  regarded  as  continuous  adjustments  of  internal  re- 
lations to  external  relations.  So  that  not  only  does  the  de- 
finition, as  thus  expressed,  comprehend  all  those  activities, 
bodily  and  mental,  which  constitute  our  ordinary  idea  of  Life ; 
but  it  also  comprehends,  both  those  processes  of  development 
by  which  the  organism  is  brought  into  general  fitness  for 
these  activities,  and  those  after-processes  of  adaptation  by  I 
which  it  is  specially  fitted  to  its  special  activities.  • — i 

Nevertheless,  superior  as  it  is  in  simplicity  and  comprehen- 
siveness, so  abstract  a  formula  as  this  is  scarcely  fitted  for 
our  present  purpose.  Reserving  its  terms  for  such  use  as  oc- 
casion may  dictate,  it  will  be  best  commonly  to  employ  its 
more  concrete  equivalent — to  consider  the  internal  relations 
as  "definite  combinations  of  simultaneous  and  successive 
changes ; "  the  external  relations  as  "  co-existences  and  se- 
quences ; "  and  the  connexion  between  them  as  a  "  corre- 
spondence." 


CHAPTER  VI. 

THE  DEGREE  OF  LIFE  VARIES  AS  THE  DEGREE  OF 
CORRESPONDENCE. 

§  31.  Already  it  has  been  shown  respecting  each  other 
qualification  included  in  the  foregoing  definition,  that  the  life 
is  high  in  proportion  as  that  qualification  is  well  fulfilled  ; 
and  it  is  now  to  be  remarked,  that  the  same  thing  is  especially 
true  respecting  this  last  qualification — the  correspondence  be- 
tween internal  and  external  relations.  It  is  manifest  dj)7'iori, 
that  since  changes  in  the  physical  state  of  the  environment,  as 
also  those  mechanical  actions  and  those  variations  of  available 
food  which  occur  in  it,  are  liable  to  stop  the  processes  going 
on  in  the  organism  ;  and  since  the  adaptive  changes  in  the 
organism  have  the  effects  of  directly  or  indirectly  counter- 
balancing these  changes  in  the  environment ;  it  follows  that 
the  life  of  the  organism  will  be  short  or  long,  low  or  high, 
according  to  the  extent  to  which  changes  in  the  environment 
are  met  by  corresponding  changes  in  the  organism.  Allow- 
ing a  margin  for  perturbations,  the  life  will  continue  only 
while  the  correspondence  continues  ;  the  completeness  of  the 
life  will  be  proportionate  to  the  completeness  of  the  corre- 
spondence ;  and  the  life  will  be  perfect  only  when  the  corre- 
spondence is  perfect.  Not  to  dwell  in  general  statements, 
however,  let  us  contemplate  this  truth  under  its  concrete 
aspects. 

§  32.  In  life  of  the  lowest  order,  we  find  that  only  the 

82 


TIIE    LIFE    VARIES    AS   THE    CORRESPONDENCE.  83 

most  prevalent  coexistences  and  sequences  in  the  environ- 
ment, have  any  simultaneous  and  successive  changes  answer- 
ing to  them  in  the  organism.  A  plant's  vital  processes 
display  adjustment  solely  to  the  continuous  coexistence  of 
certain  elements  and  forces  surrounding  its  roots  and  leaves ; 
and  vary  only  with  the  variations  produced  in  these  ele- 
ments and  forces  by  the  sun — are  unaffected  by  the  countless 
mechanical  and  other  changes  occurring  around  ;  save  when 
accidentally  arrested  by  these.  The  life  of  a  worm  is  made 
up  of  actions  referring  almost  exclusively  to  the  tangible  pro- 
perties of  adjacent  things.  All  those  visible  and  audible 
changes  which  happen  near  it,  and  are  connected  with  other 
changes  that  may  presently  destroy  it,  pass  unrecognized — 
produce  in  it  no  adapted  changes :  its  only  adjustment  of  in- 
ternal relations  to  external  relations  of  this  order,  is  seen 
when  it  escapes  to  the  surface  on  feeling  the  vibrations  pro- 
duced by  an  approaching  mole.  Adjusted  as  are  the  pro- 
ceedings of  a  bird,  to  a  far  greater  number  of  coexistences  and 
sequences  in  the  environment,  cognizable  by  sight,  hearing, 
scent,  and  their  combinations ;  and  numerous  as  are  the 
dangers  it  shuns  and  the  needs  it  fulfils,  in  virtue  of  this  ex- 
tensive  correspondence ;  it  exhibits  no  such  actions  as  those 
by  which  a  human  being  counterbalances  variations  in  tem- 
perature and  supply  of  food,  consequent  on  the  seasons.  And 
when  we  see  the  plant  eaten,  the  worm  trodden  on,  the  bird 
dead  from  starvation  ;  we  see  alike  that  the  death  is  an  arrest 
of  such  correspondence  as  existed  ;  that  it  occurred  when 
there  was  some  change  in  the  environment  to  which  the  or- 
ganism made  no  answering  change ;  and  that  thus,  both  in 
shortness  and  simplicity,  the  life  was  incomplete  in  propor- 
tion as  the  correspondence  was  incomplete.  Progress  towards 
more  prolonged  and  higher  life,  evidently  implies  an  ability 
to  respond  to  less  general  coexistences  and  sequences.  Each 
step  upwards  must  consist  in  adding  to  the  previously-adjasted 
relations  which  the  organism  exhibits,  some  further  relation 
parallel  to  a  further  relation  in  the  environment.     And  the 


8J:  THE    DATA    OF    BIOLOGY. 

greater  correspondence  thus  established,  must,  other  things 
equal,  show  itself  both  in  greater  complexity  of  life,  and 
greater  length  of  life — a  truth  which  will  be  duly  realized  on 
remembering  that  enormous  mortality  which  prevails  among 
lowly-organized  creatures,  and  that  gradual  increase  of  lon- 
gevity and  diminution  of  fertility  which  we  meet  with  on  as- 
cending to  creatures  of  higher  and  higher  development. 

It  must,  however,  be  remarked,  that  while  length  and  com- 
plexity of  life  are,  to  a  great  extent,  associated— while  a 
more  extended  correspondence  in  the  successive  changes, 
commonly  implies  increased  correspondence  in  the  simul- 
taneous changes ;  yet  it  is  not  uniformly  so.  Between  the 
two  great  divisions  of  life — animal  and  vegetal — this  contrast 
by  no  means  holds.  A  tree  may  live  a  thousand  years, 
though  the  simultaneous  changes  going  on  in  it  answer  only 
to  the  few  chemical  affinities  in  the  air  and  the  earth,  and 
though  its  serial  changes  answer  only  to  those  of  day  and 
night,  of  the  weather  and  the  seasons.  A  tortoise,  which 
exhibits  in  a  given  time  nothing  like  the  number  of  internal 
actions  adjusted  to  external  ones,  that  are  exhibited  by  a  dog, 
yet  lives  far  longer.  The  tree  by  its  massive  trunk,  and  the 
tortoise  by  its  hard  carapace,  are  saved  the  necessity  of  re- 
sponding to  those  many  surrounding  mechanical  actions  which 
organisms  not  thus  protected  must  respond  to  or  die ;  or 
rather — the  tree  and  the  tortoise  display  in  their  structures, 
certain  simple  statical  relations  adapted  to  meet  countless 
dynamical  relations  external  to  them.  But  notwithstanding 
the  qualifications  suggested  by  such  cases,  it  needs  but  to 
compare  a  microscopic  fungus  with  an  oak,  an  animalcule 
with  a  shark,  a  mouse  with  a  man,  to  recognize  the  fact  that 
this  increasing  correspondence  of  its  changes  with  those  of 
the  environment,  which  characterizes  progressing  life,  ha- 
bitually shows  itself  at  the  same  time  in  continuity  and  in 
complication. 

Even  were  not  the  connexion  between  length  of  life  and 
complexity  of  life  thus  conspicuous,  it  would  still  be  true 


THE    LIFE    VARIES    AS    THE    CORRESPONDENCE.  85 

that  the  degree  of  life  varies  with  the  degree  of  correspond- 
ence. For  if  the  lengthened  existence  of  a  tree  be  looked 
upon  as  tantamount  to  a  considerable  degree  of  life  ;  then  it 
must  be  admitted  that  its  lengthened  display  of  correspond- 
ences is  tantamount  to  a  considerable  degree  of  correspond- 
ence. If  otherwise  it  be  held,  that  notwithstanding  its  much 
shorter  existence,  a  dog  must  rank  above  a  tortoise  in  degree 
of  life,  because  of  its  superior  activity  ;  then  it  is  implied  that 
its  life  is  higher,  because  its  simultaneous  and  successive 
changes  are  more  complex  and  more  rapid — because  the 
correspondence  is  greater.  And  since  we  regard  as  the  high- 
est life,  that  which,  like  our  own,  shows  great  complexity  in 
the  correspondences,  great  rapidity  in  the  succession  of  them, 
and  great  length  in  the  series  of  them  ;  the  equivalence 
between  degree  of  life  and  degree  of  correspondence,  is  un- 
questionable. 

§  33.  In  further  elucidation  of  this  general  truth,  and 
especially  in  explanation  of  the  irregularities  just  referred  to, 
it  requires  to  be  observed,  that  as  the  life  becomes  higher 
the  environment  itself  becomes  more  complex.  Though, 
literally,  the  environment  means  all  surrounding  space  with 
the  coexistences  and  sequences  contained  in  it ;  yet,  practi- 
cally, it  often  means  but  a  small  part  of  this.  The  environ- 
ment of  an  entozoon,  can  scarcely  be  said  to  extend  beyond 
the  body  of  the  animal  in  which  the  entozoon  lives.  That  of 
a  fresh-water  alga  is,  virtually,  limited  to  the  ditch  inhab- 
ited by  the  alga.  And  understanding  the  term  in  this  re- 
stricted sense,  we  shall  see  that  the  superior  organisms 
inhabit  the  more  complicated  environments. 

Thus,  contrasted  with  that  found  on  land,  the  lower  life  is 
that  found  in  the  sea  ;  and  it  has  the  simpler  environment. 
Marine  creatures  are  affected  by  a  smaller  number  of  co- 
existences and  sequences  than  terrestrial  ones.  Being  very 
nearly  of  the  same  specific  gravity  as  the  surrounding 
medium,  they  have  to  contend  with  less  various  mechanical 


86  THE    DATA    OF   BIOLOGY. 

actions.  The  zoophyte  rooted  to  a  stone,  and  the  acalephe 
passively  borne  along  in  the  current,  need  to  undergo  no 
internal  changes  such  as  those  by  which  the  caterpillar  meets 
the  varying  effects  of  gravitation,  while  creeping  over  and 
under  the  leaves.  Again,  the  sea  is  liable  to  none 

of  those  extreme  and  rapid  alterations  of  temperature  which 
the  air  suffers.  JS'ight  and  day  produce  no  appreciable 
modifications  in  it ;  and  it  is  comparatively  little  affected  by 
the  seasons.  Thus  its  contained  fauna  show  no  marked  cor- 
respondences similar  to  those  by  which  air-breathing  crea- 
tures counterbalance  thermal  changes.  Further,  in 
respect  to  the  supply  of  nutriment  the  conditions  are  more 
simple.  The  lower  tribes  of  animals  inhabiting  the  water, 
like  the  plants  inhabiting  the  air,  have  their  food  brought  to 
them.  The  same  current  which  brings  oxygen  to  the  oyster, 
also  brings  it  the  microscopic  organisms  on  which  it 
lives  :  the  disintegrating  matter  and  the  matter  to  be  inte- 
grated, coexist  under  the  simplest  relation.  It  is  otherwise 
with  land  animals.  The  oxygen  is  everywhere  ;  but  that 
which  is  needed  to  neutralize  its  action  is  not  everywhere :  it 
has  to  be  sought ;  and  the  conditions  under  which  it  is  to  be 
obtained  are  more  or  less  complex.  So  too  with 
that  liquid  by  the  agency  of  which  the  vital  processes  are 
carried  on.  To  marine  creatures,  water  is  ever  present,  and  by 
the  lowest  is  passively  absorbed  ;  but  to  most  creatures  living 
on  the  earth  and  in  the  air,  it  is  made  available  only  through 
those  nervous  changes  constituting  perception,  and  those 
muscular  ones  by  which  drinking  is  effected.  Simi- 
larly, the  contrast  might  be  continued  with  respect  to  the 
electric  and  hygrometric  variations  ;  and  the  greater  multi- 
plicity of  optical  and  acoustic  phenomena  with  which  ter- 
restrial life  is  surrounded.  And  tracing  upwards  from  the 
amphibia  the  widening  extent  and  complexity  which  the 
environment,  as  practically  considered,  assumes — observing 
further  how  increasing  heterogeneity  in  the  flora  and  fauna 
of  the  globe,  itself  progressively  complicates  the  environment 


THE    LIFE    VARIES    AS   THE    CORRESPONDENCE.  87 

of  each  species  of  organism — it  might  finally  be  shown  that 
the  same  general  truth  is  displayed  in  the  history  of  mankind  : 
whose  advance  in  civilization  has  been  simultaneous  with 
their  advance  from  the  less  varied  requirements  of  the  torrid 
zone  to  the  more  varied  requirements  of  the  temperate  zone ; 
whose  chief  steps  have  been  made  in  regions  presenting  a 
complicated  physical  geography ;  and  who,  in  the  course  of 
their  progress,  have  been  adding  to  their  physical  environ- 
ment a  social  environment  that  has  been  growing  even  more 
involved.  Thus,  speaking  generally,  it  is  clear  that  those  re- 
lations in  the  environment  to  which  relations  in  the  organism 
must  correspond,  themselves  increase  in  number  and  intricacy 
as  the  life  assumes  a  higher  form. 

§  3-i.  To  make  yet  more  manifest  the  fact,  that  the  degree 
of  life  varies  as  the  degree  of  correspondence,  I  may  here 
point  out,  that  those  other  distinctions  successively  noted 
when  contrasting  vital  changes  with  non-vital  changes,  are 
all  implied  in  this  last  distinction — their  correspondence 
with  external  co-existences  and  sequences.  And  to  this  may 
be  added  the  supplementary  fact,  that  the  increasing  fulfil- 
ment of  those  other  distinctions  which  we  found  to  accompany 
increasing  life,  is  involved  in  the  increasing  fulfilment  of  this 
last  distinction.  To  descend  to  particulars : — We  saw  that 
living  organisms  are  characterized  by  successive  changes  ; 
and  that  as  the  life  becomes  higher,  the  successive  changes 
become  more  numerous.  "Well,  the  environment  is  full  of 
successive  changes,  both  positive  and  relative ;  and  the 
greater  the  correspondence,  the  greater  the  number  of  suc- 
cessive changes  an  organism  must  display.  We  saw  that  life 
presents  simultaneous  changes ;  and  that  the  more  elevated 
it  is,  the  more  marked  the  multiplicity  of  them.  Well, 
besides  countless  phenomena  of  coexistence  in  the  environ- 
ment, there  are  often  many  changes  occurring  in  it  at  the 
same  moment ;  and  hence  increased  correspondence  with  it, 
supposes  an  increased  display  of  simultaneous  changes  in  the 


88  THE   DATA    OF   BIOLOGY. 

organism.  Similarly  with  the  heterogeneity  of  the  changes. 
In  the  environment  the  relations  are  very  varied  in  their 
kinds;  and  hence,  as  the  organic  actions  come  more  and  more 
into  correspondence  with  them,  they  also  must  become  very 
varied  in  their  kinds.  So  again  is  it,  even  with  definiteness 
of  combination.  For  though  the  inorganic  bodies  of  wThich 
the  environment  mainly  consists,  do  not  present  definitely- 
combined  changes,  yet  they  present  definitely-combined 
properties ;  and  thoguh  the  minor  meteorologic  variations  of 
the  environment,  do  not  show  much  definiteness  of  combina- 
tion, yet  those  resulting  from  day  and  night  and  the  seasons 
do.  Add  to  which,  that  as  the  environment  of  each  organism 
comprehends  all  those  other  organisms  existing  within  its 
sphere  of  life — as  the  most  important  and  most  numerous 
surrounding  changes  with  which  each  animal  has  to  deal, 
are  the  definitely-combined  changes  exhibited  by  other  ani- 
mals, whether  prey  or  enemies ;  it  results  that  definiteness 
of  combination  is  a  general  characteristic  of  the  external 
changes  with  which  internal  ones  have  to  correspond.  Hence, 
increase  of  correspondence  involves  increased  definiteness  of 
combination.  So  that  throughout,  the  correspondence  of 
the  internal  relations  with  the  external  ones,  is  the  essential 
thing ;  and  all  the  special  characteristics  of  the  internal  rela- 
tions, are  but  the  collateral  results  of  this  correspondence. 

§  35.  As  affording  the  simplest  and  most  conclusive  proof 
that  the  degree  of  life  varies  as  the  degree  of  correspondence, 
it  remains  to  point  out  that  perfect  correspondence  would  be 
perfect  life.  Were  there  no  changes  in  the  environment  but 
such  as  the  organism  had  adapted  changes  to  meet ;  and  were 
it  never  to  fail  in  the  efficiency  with  which  it  met  them  ;  there 
would  be  eternal  existence  and  universal  knowledge.  Death 
by  natural  decay,  occurs  because  in  old  age  the  relations  be- 
tween assimilation,  oxidation,  and  genesis  of  force  going  on 
in  the  organism,  gradually  fall  out  of  correspondence  with  the 
relations  between  oxygen  and  food  and  absorption  of  heat  by 


THE    LIFE    VARIES    AS   THE    CORRESPONDENCE.  89 

the  environment.  Death  from  disease,  arises  either  when  the 
organism  is  congenitally  defective  in  its  power  to  balance  the 
ordinary  external  actions  by  the  ordinary  internal  actions,  or 
when  there  has  taken  place  some  unusual  external  action  to 
which  there  was  no  answering  internal  action.  Death  by 
accident,  implies  some  neighbouring  mechanical  changes  of 
which  the  causes  are  either  unobserved  from  inattention,  or 
are  so  intricate  that  their  results  cannot  be  foreseen ;  and 
consequently  certain  relations  in  the  organism  are  not  adjusted 
to  the  relations  in  the  environment.  Manifestly,  if,  to  every 
outer  coexistence  and  sequence  by  which  it  was  ever  in  any 
degree  affected,  the  organism  presented  an  answering  process 
or  act ;  the  simultaneous  changes  would  be  indefinitely  nu- 
merous and  complex,  and  the  successive  ones  endless — the 
correspondence  would  be  the  greatest  conceivable,  and  the 
life  the  highest  conceivable,  both  in  degree  and  in  length. 

§  36.  Before  closing  the  chapter,  it  will  be  useful  to  com- 
pare the  definition  of  Life  here  set  forth,  with  the  defini- 
tion of  Evolution  set  forth  in  First  Principles.  Living 
bodies  being  bodies  which  display  in  the  highest  degree  the 
structural  changes  constituting  Evolution ;  and  Life  being 
made  up  of  the  functional  changes  that  accompany  these 
structural  changes ;  we  ought  to  find  a  certain  harmony 
between  the  definitions  of  Evolution  and  of  Life.  Such  a 
harmony  is  not  wanting. 

The  first  distinction  we  noted  between  the  kind  of  change 
shown  in  Life,  and  other  kinds  of  change,  was  its  serial 
character :  we  saw  that  vital  change  is  substantially  unlike 
non-vital  change,  in  being  made  up  of  successive  changes. 
Xow  since  organic  bodies  display  in  so  much  higher  a  de- 
gree than  inorganic  bodies,  those  continuous  differentiations 
and  integrations  which  constitute  Evolution  ;  and  since  the 
re-distributions  of  matter  thus  carried  so  far  in  a  compara- 
tively short  period,  imply  concomitant  re-distributions  of  mo- 
tion ;  it  is  clear  that  in  a  given  time,  organic  bodies  must 


90  THE    DATA    OF    BIOLOGY. 

undergo  changes  so  comparatively  numerous  as  to  render  the 
successiveness  of  their  changes  a  marked  characteristic.  And 
it  will  follow  a  priori,  as  we  found  it  to  do  d  posteriori,  that 
the  organisms  exhibiting  Evolution  in  the  highest  degree, 
exhibit  the  longest  or  the  most  rapid  succession  of  changes, 
or  both.  Again,  it  was  shown  that  vital  change  is 

distinguished  from  non-vital  change  by  being  made  up  of 
many  simultaneous  changes ;  and  also  that  creatures  possess- 
ing high  vitality  are  marked  off  from  those  possessing  low 
vitality,  by  the  far  greater  number  of  their  simultaneous 
changes.  Here  too  there  is  entire  congruity.  In  First 
Principles,  §  116,  we  reached  the  conclusion,  that  a  force 
falling  on  any  aggregate  is  divided  into  several  forces ;  that 
when  the  aggregate  consists  of  parts  that  are  unlike,  each 
part  becomes  a  centre  of  unlike  differentiations  of  the  inci- 
dent force ;  and  that  thus  the  multiplicity  of  such  differen- 
tiations must  increase  with  the  multiplicity  of  the  unlike 
parts.  It  follows  necessarily,  therefore,  that  organic  aggre- 
gates, which  as  a  class  are  distinguished  from  inorganic 
aggregates  by  the  greater  number  of  their  unlike  parts,  must 
be  also  distinguished  from  them  by  the  greater  number  of 
simultaneous  changes  they  display ;  and  further  that  the 
higher  organic  aggregates,  having  more  numerous  unlike 
parts  than  the  lower,  must  undergo  more  numerous  simul- 
taneous changes.  "We  next  found  that  the  changes 
occurring  in  living  bodies,  are  contrasted  with  those  occurring 
in  other  bodies,  as  being  much  more  heterogeneous  /  and  that 
the  changes  occurring  in  the  superior  living  bodies,  are 
similarly  contrasted  with  those  occurring  in  inferior  ones. 
Well,  heterogeneity  of  function  is  the  correlate  of  hetero- 
geneity of  structure ;  and  heterogeneity  of  structure  is  the 
leading  distinction  between  organic  and  inorganic  aggre- 
gates, as  well  as  between  the  more  highly  organized  and  the 
more  lowly  organized.  By  reaction,  an  incident  force  must 
be  rendered  multiform  in  proportion  to  the  multiformity  of 
the  aggregate  on  which  it  falls ;  and  hence  those  most  mul- 


THE    LIFE    VARIES    AS    THE    CORRESPONDENCE.  91 

tiform  aggregates  which  display  in  the  highest  degree  the 
phenomena  of  Evolution  structurally  considered,  must  at  the 
same  time  be  aggregates  which  display  in  the  highest  de- 
gree the  multiform  actions  which  constitute  Evolution 
functionally  considered.  These  heterogeneous  changes, 

exhibited  simultaneously  and  in  succession  by  a  living  or- 
ganism, prove,  on  further  inquiry,  to  be  distinguished  by 
their  combination  from  certain  non-vital  changes  which 
simulate  them.  Here,  too,  the  parallelism  is  maintained. 
It  was  shown  in  §  56  of  First  Principles,  that  an  essential 
characteristic  of  Evolution  is  the  integration  of  parts,  which 
accompanies  their  differentiation — an  integration  that  is 
shown  both  in  the  consolidation  of  each  part,  and  in  the 
consolidation  of  all  the  parts  into  a  whole.    Now,  manifestly, 

combination  anions;  the  changes  going;  on  in  different  coin- 
ed c?         o         o 

bined  parts,  must  be  proportionate  to  the  degree  of  com- 
bination among  these'  parts  :  the  more  mutually  dependent 
the  parts,  the  more  mutually-dependent  must  be  their 
actions.  Hence,  animate  bodies  having  greater  co-ordin- 
ation of  parts  than  inanimate  ones,  must  exhibit  greater 
co-ordination  of  changes.  And  this  greater  co-ordination  of 
their  changes  must  not  only  distinguish  organic  from  inor- 
ganic aggregates  ;  but  must,  for  the  same  reason,  distinguish 
higher  organisms  from  lower  ones,  as  we  found  that  it 
did.  Yet  once  more,  it  was  pointed  out  that   the 

changes  constituting  Life,  differ  from  other  changes  in  the 
d'tiniteness  of  their  combination  ;  and  that  a  distinction  like  in 
kind,  though  less  in  degree,  holds  between  the  vital  changes 
of  superior  creatures  and  those  of  inferior  creatures.  These, 
also,  are  contrasts  in  harmony  with  the  contrasts  disclosed  by 
the  analysis  of  Evolution.  We  saw  {First  Principles,  §§  54, 
55)  that  during  Evolution,  there  is  an  increase  of  definiteness 
as  '.veil  as  an  increase  of  heterogeneity.  We  saw  that  the 
integration  accompanying  differentiation,  has  necessarily  the 
effect  of  increasing  the  distinctness  with  which  the  parts  are 
marked  off  from  each  other  ;  and  that  so,  out  of  the  inco- 


92  THE   DATA   OF   BIOLOGY. 

herent  and  indefinite,  there  arises  the  coherent  and  definite. 
But  a  coherent  whole  made  up  of  definite  parts  definitely 
combined,  must  exhibit  more  definitely  combined  changes 
than  a  whole  made  up  of  parts  that  are  neither  definite  in 
themselves  nor  in  their  combination.  Hence,  if  living  bodies 
display  more  than  other  bodies  this  structural  definiteness, 
then,  definiteness  of  combination  must  be  a  characteristic  of 
the  changes  constituting  Life  ;  and  must  also  distinguish  the 
vital  changes  of  higher  organisms  from  those  of  lower  organ- 
isms. Finally,  however,  we  discovered  that  all  these 
peculiarities  are  subordinate  to  the  one  fundamental  pecu- 
liarity, that  vital  changes  take  place  in  correspondence  with 
external  co-existences  and  sequences ;  and  that  the  highest 
possible  Life  is  reached,  when  there  is  some  inner  relation  of 
actions  fitted  to  meet  every  outer  relation  of  actions  by 
which  the  organism  can  be  affected.  But  this  conception  of 
the  highest  possible  Life,  is  in  perfect  harmony  with  the  con- 
ception, before  arrived  at,  of  the  ultimate  limit  of  Evolution. 
When  treating  of  equilibration  as  exhibited  in  organic 
phenomena  {First  Principles,  §§  133,  134),  it  was  pointed 
out,  that  the  continual  tendency  is  towards  the  establishment 
of  a  balance  between  inner  and  outer  changes.  It  was 
shown  that  "  the  final  structural  arrangements  must  be  such 
as  will  meet  all  the  forces  acting  on  the  aggregate,  by 
equivalent  antagonistic  forces,"  and  that  "the  maintenance 
of  such  a  moving  equilibrium "  as  an  organism  displays, 
"  requires  the  habitual  genesis  of  internal  forces  correspond- 
ing in  number,  directions,  and  amounts,  to  the  external 
incident  forces — as  many  inner  functions,  single  or  com- 
bined, as  there  are  single  or  combined  outer  actions  to  be 
met."  It  was  shown,  too,  that  the  relations  among  concep- 
tions and  ideas,  are  ever  in  progress  towards  a  better  balance 
between  mental  actions  and  those  actions  in  the  environment 
to  which  conduct  must  be  adjusted.  So  that  that  main- 
tenance of  a  correspondence  between  inner  and  outer  rela- 
tions, which  we  have  here  found  to  constitute  Life,  and  the 


THE    LIFE    VARIES    AS    THE    CORRESPONDENCE.  93 

perfection  of  which  is  the  perfection  of  Life,  answers  com- 
pletely to  that  state  of  organic  moving  equilibrium  which 
we  saw  arises  in  the  course  of  Evolution,  and  tends  ever  to 
become  more  complete. 

There  is  much  significance  in  this  complete  parallelism. 
That  two  inquiries  starting  from  different  points  and  carried 
on  in  different  ways,  should  lead  to  conclusions  so  entirely 
harmonizing  with  each  other,  cannot  fail  further  to  confirm 
these  conclusions;  if  further  confirmation  of  them  be  needed. 


CHAPTER  VII. 

THE  SCOPE  OF  BIOLOGY. 

§  37.  We  are  now  in  a  position  to  map  ont  the  boundaries 
and  divisions  of  our  subject.  Grouping  together  the  general 
results  arrived  at  in  the  first  three  chapters,  and  joining  with 
them  the  results  which  the  last  three  chapters  have  brought  us 
to,  we  shall  be  prepared  to  comprehend  the  science  of  Biology 
as  a  whole ;  and  to  see  how  its  truths  may  best  be  classified. 

In  the  chapters  treating  of  Organic  Matter,  the  Actions  of 
Forces  on  it,  and  its  Reactions  on  Forces,  the  generalizations 
reached  were  these  : — that  organic  matter  is  specially  sensi- 
tive to  surrounding  agencies  ;  that  in  consequence  of  the 
extreme  instability  of  the  compounds  it  contains,  minute  dis- 
turbances can  cause  in  it  large  amounts  of  re-distribution  ; 
and  that  during  the  fall  of  its  unstably-arranged  atoms  into 
stable  arrangements,  there  are  given  out  proportionately 
large  amounts  of  motion.  We  saw  that  organic  matter  is  so 
constituted,  that  small  incident  actions  are  capable  of  initiat- 
ing great  reactions— setting  up  extensive  structural  modifica- 
tions, and  liberating  large  quantities  of  power.  In 
the  chapters  just  concluded,  the  changes  of  which  Life  is 
made  up,  were  shown  to  be  so  adjusted  as  to  balance  outer 
changes.  And  the  general  process  of  the  adjustment  we 
found  resolves  itself  into  this ;  that  if  in  the  environment 
there  are  any  related  actions,  A  and  B,  by  which  the  or- 

94 


THE    SCOPE    OF    BIOLOGY.  95 

ganism  is  affected,  then  if  A  produces  in  the  organism  some 
change  #,  there  follows  in  the  organism  some  change  b,  fitted 
in  time,  direction,  and  amount  to  meet  the  action  B — a 
change  which  is  often  required  to  he  much  larger  than  its 
antecedent.  Mark,  now,  the  relation  between  these 

two  final  results.  On  the  one  hand,  for  the  maintenance  of 
that  correspondence  between  inner  and  outer  actions  which 
constitutes  Life,  an  organism  must  be  susceptible  to  small 
changes  from  small  external  forces  (as  in  sensation),  and  must 
be  able  to  initiate  large  changes  in  opposition  to  large  external 
forces  (as  in  muscular  action).  On  the  other  hand,  organic 
matter  is  at  once  extremely  sensitive  to  disturbing  agencies 
of  all  kinds,  and  is  capable  of  suddenly  evolving  motion  in 
great  amounts.  That  is  to  say,  the  constitution  of  organic 
matter  specially  adapts  it  to  receive  and  produce  the  internal 
changes  required  to  balance  external  changes. 

This  being  the  general  character  of  the  vital  Functions, 
and  of  the  Matter  in  which  they  are  performed,  the  science 
of  Biology  becomes  an  account  of  all  the  phenomena  attend- 
ant on  the  performance  of  such  Functions  by  such  Matter — 
an  account  of  all  the  conditions,  concomitants,  and  conse- 
quences, under  the  Various  circumstances  fallen  into  by  living 
bodies.  If  all  the  functional  phenomena  which  living  bodies 
present,  are,  as  we  have  concluded,  incidents  in  the  main- 
tenance of  a  correspondence  between  inner  and  outer  ac- 
tions ■  and  if  all  the  structural  phenomena  which  living 
bodies  present,  are  direct  or  indirect  concomitants  of  func- 
tional phenomena ;  then  the  entire  Science  of  Life,  must  con- 
sist in  a  detailed  interpretation  of  all  these  functional  and 
structural  phenomena  in  their  relations  to  the  phenomena  of 
the  environment.  Immediately  or  mediately,  proximately 
or  remotely,  every  trait  exhibited  by  organic  bodies,  as 
distinguished  from  inorganic  bodies,  must  be  referable  to 
this  continuous  adjustment  between  their  actions  and  the 
actions  going  on  around  them.  Such  being  the  extent  and 
nature  of  our  subject-matter,  it  may  be  thus  divided. 


96  THE    DATA    OF   BIOLOGY. 

1.  An  account  of  the  structural  phenomena  presented  by 
organisms.     And  this  subdivides  into  : — 

a.  The  structural  phenomena  presented  by  individual 
organisms. 

b.  The  structural  phenomena  presented  by  successions 
of  organisms. 

2.  An  account  of  the  functional  phenomena  which  or- 
ganisms present.    And  this,  too,  admits  of  sub-division  into : — 

a.  The  functional  phenomena  of  individual  organisms. 

b.  The  functional  phenomena  of.  successions  of  organisms. 

3.  An  account  of  the  actions  of  Structure  on  Function, 
and  the  re-actions  of  Function  on  Structure.  And  like  the 
others,  this  is  divisible  into  : — 

a.  The  actions  and  re-actions  as  exhibited  in  individual 
organisms. 

b.  The  actions  and  re-actions  as  exhibited  in  successions 
of  organisms. 

4.  An  account  of  the  phenomena  attending  the  production 
of  successions  of  organisms  :  in  other  words — the  phenomena 
of  Genesis. 

There  is,  indeed,  another  mode  of  grouping  the  facts  of 
Biology,  with  which  all  are  familiar.  According  as  they 
are  facts  of  animal  or  vegetal  life,  they  may  be  classed 
under  the  heads  of  Zoology  and  Botany.  But  this  di- 
vision, though  convenient  and  indeed  necessary  for  practi- 
cal purposes,  is  one  that  does  not  here  concern  us.  Dealing 
with  organic  structures  and  functions  in  connexion  with 
their  causes,  conditions,  concomitants,  and  consequences, 
Biology  cannot  divide  itself  into  Animal-Biology  and  Vege- 
tal-Biology ;  since  the  same  fundamental  classes  of  phe- 
nomena are  common  to  both.  Eecognizing  this  familiar 
distinction  only  as  much  as  convenience  obliges  us  to  do,  let 
us  now  pass  on  to  consider,  more  in  detail,  the  classification 
of  biologic  phenomena,  above  set  down  in  its  leading  outlines. 

§  38.    The    facts    of    structure    which    an    individual    or- 


THE    SCOPE   OF    BIOLOGY.  97 

ganism  exhibits,  are  of  two  chief  kinds.  In  order  of  con- 
spicnousness,  though  not  in  order  of  time,  there  come  first 
those  ultimate  arrangements  of  parts  which  characterize  the 
organism  in  its  mature  state — an  account  of  which,  commonly 
called  Anatomy,  is  more  properly  called  Morphology.  And 
second,  there  come  those  successive  modifications  through 
which  the  organism  passes  in  its  development  from  the  germ 
to  the  adult  form — an  account  of  which  is  called  Embryology. 

The  facts  of  structure  which  any  succession  of  individual 
organisms  exhibits,  admit  of  similar  classification.  On  the 
one  hand,  we  have  those  inner  and  outer  differences  of  shape, 
that  are  liable  to  arise  between  the  adult  members  of  suc- 
cessive generations  descended  from  a  common  stock — differ- 
ences which,  though  usually  not  marked  between  adjacent 
generations,  may  in  course  of  many  generations  become  great. 
And  on  the  other  hand,  we  have  those  developmental  modi- 
fications through  which  such  modifications  of  the  descended 
forms  are  reached. 

The  interpretation  of  structure,  as  exhibited  in  individual 
organisms  and  successions  of  organisms,  is  aided  by  two  sub- 
sidiary divisions  of  biologic  inquiry,  named  Comparative 
Anatomy  (properly  Comparative  Morphology)  and  Compara- 
tive Embryology.  These  cannot  properly  be  regarded  as  in 
themselves  parts  of  Biology  ;  since  the  facts  embraced  under 
them  are  not  substantive  phenomena,  but  are  simply  inci- 
dental to  substantive  phenomena.  All  the  facts  of  structural 
Biology  are  comprehended  under  the  two  foregoing  sub- 
divisions ;  and  the  comparison  of  these  facts  as  presented 
in  different  classes  of  organisms,  is  simply  a  method  of  inter- 
preting the  real  relations  and  dependencies  of  the  facts  com- 
pared. 

Nevertheless,  though  Comparative  Morphology  and  Com- 
parative Embryology  do  not  disclose  additional  series  of  con- 
crete or  special  facts,  they  lead  to  the  establishment  of  certain 
abstract  or  general  facts.  By  them  it  is  made  manifest  that 
underneath  the  superficial  differences  of  groups  and  classes 


98  THE   DATA    OF   BIOLOGY. 

and  types  of  organisms,  there  are  hidden  fundamental  simi- 
larities ;  and  that  the  courses  of  development  in  such  groups 
and  classes  and  types,  though  in  many  respects  divergent, 
are  in  some  essential  respects,  coincident.  The  wide  truths 
thus  disclosed,  come  under  the  heads  of  General  Morphology 
and  General  Embryology. 

By  contrasting  the  structures  of  organisms,  there  is  also 
achieved  that  grouping  of  the  like  and  separation  of  the 
unlike,  called  Classification.  First  by  observation  of  ex- 
ternal characters ;  second  by  observation  of  internal  charac- 
ters ;  and  third  by  observation  of  the  phases  of  development ; 
it  is  ascertained  what  organisms  are  most  similar  in  all 
particulars  ;  what  organisms  are  like  each  other  in  every 
important  attribute  ;  what  organisms  have  common  primor- 
dial characters.  Whence  there  finally  results  such  an  ar- 
rangement of  organisms,  that  if  certain  structural  attributes 
of  any  one  be  given,  its  other  structural  attributes  may  be 
empirically  predicted  ;  and  which  prepares  the  way  for  that 
interpretation  of  their  relations  and  genesis,  which  forms  an 
important  part  of  rational  Biology. 

§  39.  The  second  main  division  of  Biology,  above  de- 
scribed as  embracing  the  functional  phenomena  of  organ- 
isms, is  that  which  is  in  part  signified  by  Physiology  :  the  re- 
mainder being  what  we  distinguish  as  Psychology.  Both  of 
these  fall  into  subdivisions  that  may  best  be  treated  sepa- 
rately. That  part  of  Physiology  which  is  concerned 
with  the  molecular  changes  going  on  in  organisms,  is  known 
as  Organic  Chemistry.  An  account  of  the  modes  in  which  the 
force  generated  in  organisms  by  chemical  change,  is  trans- 
formed into  other  forces,  and  made  to  work  the  various  or- 
gans that  carry  on  the  functions  of  Life,  comes  under  the 
head  of  Organic  Physics.  Psychology,  which  is 
mainly  concerned  with  the  adjustment  of  vital  actions  to 
actions  in  the  environment  (in  contrast  with  Physiology, 
which  is  mainly  concerned  with  vital   actions   apart   from 


THE   SCOPE   OF   BIOLOGY.  99 

actions  in  the  environment)  consists  of  two  quite  distinct  por- 
tions. Objective  Psychology  deals  with  those  functions  of  the 
nervo-muscular  apparatus  by  which  such  organisms  as  possess 
it,  are  enabled  to  adjust  inner  to  outer  relations ;  and  includes 
also,  the  study  of  the  same  functions  as  externally  manifested 
in  conduct.  Subjective  Psychology  deals  with  the  sensations, 
perceptions,  ideas,  emotions,  and  volitions  that  are  the  direct 
or  indirect  concomitants  of  this  visible  adjustment  of  inner 
to  outer  relations — considers  these  several  kinds  of  conscious- 
ness in  their  genesis,  and  their  connexions  of  co-existence  and 
succession.  Consciousness  under  its  different  modes  and 
forms,  being  a  subject-matter  radically  distinct  in  nature  from 
the  subject-matter  of  Biology  in  general ;  and  the  method  of 
self-analysis,  by  which  alone  the  laws  of  dependence  among 
changes  of  consciousness  can  be  found,  being  a  method  un- 
paralleled by  anything  in  the  rest  of  Biology  ;  we  are 
obliged  to  regard  Subjective  Psychology  as  a  separate  study 
— not  absolutely,  of  course,  but  relatively  to  the  mind  of  each 
student.  And  since  it  would  be  very  inconvenient  to  dis- 
sociate Objective  Psychology  from  Subjective  Psychology, 
we  are  practically  compelled  to  deal  with  the  two  as  forming 
an  independent  sub-science,  to  be  treated  apart  from  the  lower 
divisions  of  Biology. 

Obviously,  the  functional  phenomena  presented  in  succes- 
sions of  organisms,  similarly  divide  into  physiological  and 
psychological.  Under  the  physiological,  come  the 

modifications  of  bodily  actions  that  arise  in  the  course  of 
generations,  as  concomitants  of  structural  modifications  ;  and 
these  may  be  modifications,  qualitative  or  quantitative,  in 
the  molecular  changes  classed  as  chemical,  or  in  the  organic 
actions  classed  as  physical,  or  in  both.  Under  the 

psychological,  come  the  qualitative  and  quantitative  modifica- 
tions of  instincts,  feelings,  conceptions,  and  mental  changes 
in  general,  that  occur  in  creatures  having  more  or  less 
intelligence,  when  certain  of  their  conditions  are  changed. 
This,  like  the  preceding  department  of  Psychology,  has  in 


100  THE   DATA   OF   BIOLOGY. 

the  abstract  two  different  aspects — the  objective  and  the  sub- 
jective. Practically,  however,  the  objective,  which  deals 
with  these  mental  modifications  as  exhibited  in  the  changing 
habits  and  abilities  of  successive  generations  of  creatures,  is 
the  only  one  that  admits  of  scientific  investigation  ;  since  the 
corresponding  alterations  in  consciousness,  cannot  be  imme- 
diately known  to  any  but  the  subjects  of  them.  Evidently, 
convenience  requires  us  to  class  this  part  of  Psychology  along 
with  the  other  parts,  in  a  distinct  sub-science. 
"""Light  is  thrown  on  functions,  as  well  as  on  structures, 
by  comparing  organisms  of  different  kinds.  Comparative 
Physiology  and  Comparative  Psychology,  are  the  names 
given  to  those  collections  of  facts  respecting  the  homologies 
and  analogies,  bodily  and  mental,  that  are  brought  to  light  by 
this  kind  of  inquiry.  These  classified  observations  concern- 
ing likenesses  and  differences  of  functions,  are  helpers  to 
interpret  functions  in  their  essential  natures  and  relations. 
Hence  Comparative  Physiology  and  Comparative  Psychology 
are  names  of  methods,  rather  than  names  of  true  sub-divisions 
of  Biology. 

Here,  however,  as  before,  the  comparison  of  special  truths, 
besides  facilitating  their  interpretation,  brings  to  light  certain 
general  truths.  Contrasting  bodily  and  mental  functions  as 
exhibited  in  various  orders  of  organisms,  shows  that  there 
exists,  more  or  less  extensively,  a  community  of  processes 
and  methods.  Hence  result  two  groups  of  abstract  propo- 
sitions, constituting  General  Physiology  and  General  Psy- 
chology. 

§  40.  In  these  various  divisions  and  sub-divisions  of  the 
first  two  great  departments  of  Biology,  the  phenomena  of 
Structure  are  considered  separately  from  the  phenomena  of 
Function,  so  far  as  separate  treatment  of  them  is  possible. 
The  third  great  department  of  Biology  deals  with  them  in 
their  necessary  connexions.     It  comprehends  the  determin- 


THE    SCOPE   OF   BIOLOGY.  101 

ation  of  functions  by  structures,  and  the  determination  of 
structures  by  functions.  r__ 

As  displayed  in  individual  organisms,  the  action  of  struc- 
tures on  functions  is  to  be  studied,  not  only  in  the  broad  and 
familiar  fact  that  the  general  kind  of  life  an  organism  leads 
is  necessitated  by  the  main  characters  of  its  organization,  but 
in  the  more  special  and  less  conspicuous  fact,  that  between 
members  of  the  same  species  minor  differences  of  structure  lead 
to  minor  differences  of  power  to  perform  certain  kinds  of  action, 
and  of  tendency  to  perform  such  kinds  of  action.  Con- 

versely, under  the  re-actions  of  function  on  structure  as 
displayed  in  individual  organisms,  come  the  facts  slewing 
that  functions,  when  fulfilled  to  their  normal  extents,  main- 
tain integrity  of  structure  in  their  respective  organs ;  and 
that  within  certain  limits,  the  increase  of  functions  is  followed 
by  such  structural  changes  in  their  respective  organs,  as  en- 
ables the  organs  to  discharge  better  their  extra  functions. 

Inquiry  into  the  action  of  structure  on  function  as  dis- 
played  in  successions  of  organisms,  introduces  us  to  such 
phenomena  as  Mr.  Darwin's  "  Origin  of  Species  "  deals  with. 
In  this  category  come  all  proofs  of  the  general  truth,  that 
when  an  individual  is  enabled  by  a  certain  structural  pecu- 
liarity, to  perform  better  than  others  of  its  species  some 
advantageous  action ;  and  when  it  bequeaths  more  or  less  of 
its  structural  peculiarity  to  descendants,  among  whom  those 
which  have  it  most  markedly,  are  best  able  to  thrive  and 
propagate ;  there  arises  through  this  continuous  action  of 
structure  on  function,  a  visibly  modified  type  of  structure, 
having  a  more  or  less  distinct  function.  In  the  cor- 

relative class  of  facts,  which  come  under  the  category  of  re- 
actions of  function  on  structure  as  exhibited  in  successions  of 
organisms,  are  to  be  placed  all  those  modifications  of  struc- 
ture which  arise  in  races,  when  changes  of  conditions  entail 
changes  in  the  balance  of  their  functions.  Here  is  to  be 
studied  the  way  in  which  altered  function  externally  necessi- 


102  THE   DATA    OF   BIOLOGY. 

tated,  works,  byre-action,  altered  structure ;  and  how  in  succeed- 
ing generations,  this  altered  structure  may  be  made  continu- 
ally more  marked  by  this  altered  function.  Though 
logically  distinct,  these  two  sub-divisions  of  biologic  inquiry 
cannot  in  practice  be  carried  on  apart.  A  speciality  of  struc- 
ture which  leads  to  an  excess  of  function  in  any  direction, 
is,  by  the  perpetual  re-action  of  function,  rendered  ever  more 
decided.  A  speciality  of  function,  by  calling  forth  a  corre- 
sponding speciality  of  structure,  produces  an  increasingly 
efficient  discharge  of  such  function.  Whichever  of  the  two 
initiates  the  change,  there  goes  on  between  them  an  unceas- 
ing action  and  re-action,  producing  in  them  co-ordinate 
modifications. 

§  41.  The  fourth  great  division  of  Biology,  comprehend- 
ing the  phenomena  of  Genesis,  may  be  conveniently  separated 
into  three  sub-divisions. 

Under  the  first,  comes  a  description  of  all  the  special 
modes  whereby  the  multiplication  of  organisms  is  carried  on  : 
which  modes  range  themselves  under  the  two  chief  heads  of 
sexual  and  asexual.  An  account  of  Sexual  Multiplication  in- 
cludes the  various  methods  by  which  germs  and  ova  are 
fertilized,  and  by  which,  after  fertilization,  they  are  furnished 
with  the  materials,  and  maintained  in  the  conditions,  needful 
for  their  development.  An  account  of  Asexual  Multiplica- 
tion includes  the  various  methods  by  which,  from  the  same 
fertilized  germ  or  ovum,  there  are  produced  many  organisms 
that  are  partially  or  totally  independent  of  each  other. 

The  second  of  these  sub-divisions  deals  with  the  phenomena 
of  Genesis  in  the  abstract.  It  takes  for  its  subject-matter,  such 
general  questions  as — What  is  the  end  subserved  by  the 
union  of  sperm-cell  and  germ-cell  ?  Why  cannot  all  multi- 
plication be  carried  on  after  the  asexual  method  ?  What 
are  the  laws  of  hereditary  transmission  ?  What  are  the  causes 
of  variation  % 

The  third  sub-division  is  devoted  to  still  more  abstract 


THE    SCOPE    OF    BIOLOGY.  103 

aspects  of  the  phenomena.  Recognizing  the  general  facts  of 
multiplication  without  reference  to  their  modes  or  immediate 
causes,  it  concerns  itself  simply  with  the  different  rates  of 
multiplication  in  different  kinds  of  organisms,  and  different 
individuals  of  the  same  kind.  Generalizing  the  numerous 
contrasts  and  variations  of  fertility,  it  seeks  a  rationale  of 
them  in  their  relations  to  other  organic  phenomena. 

§  42.  Such  appears  to  be  the  natural  arrangement  of 
divisions  and  sub-divisions  which  Biology  presents,  when  re- 
garded from  the  highest  point  of  view,  as  the  Science  of 
Life — the  science  which  has  for  its  subject-matter,  the  cor- 
respondence of  organic  relations,  with  the  relations  amid 
which  organisms  exist.  This,  however,  is  a  classification  of 
the  parts  of  Biology  when  fully  developed ;  rather  than  a 
classification  of  the  parts  of  Biology  as  it  now  stands. 
Several  of  the  sub-divisions  above  named  have  no  recognized 
existence  ;  and  sundry  of  the  others  are  in  quite  rudimentary 
states.  It  is  therefore  impossible  now  to  fill  in,  even  in  the 
roughest  way,  more  than  a  part  of  the  outlines  here 
sketched. 

Our  course  of  inquiry  being  thus  in  great  measure  de- 
termined by  the  present  state  of  knowledge,  we  are  com- 
pelled to  follow  an  order  widely  different  from  this  ideal  one. 
It  will  be  necessary  first  to  give  an  account  of  those  empiri- 
cal generalizations  which  naturalists  and  physiologists  have 
established :  arranging  them  rather  with  a  view  to  facility 
of  comprehension  than  to  logical  sequence ;  and  append- 
ing to  those  which  admit  of  it,  such  deductive  interpreta- 
tions as  First  Principles  furnish  us  with.  Having  done  this, 
we  shall  be  the  better  prepared  for  dealing  with  the  lead- 
ing truths  of  Biology,  in  connexion  with  the  doctrine  of 
Evolution. 


PART    II. 


THE   INDUCTIONS  OF  BIOLOGY. 


CHAPTER  I. 

GROWTH. 

$  43.  Perhaps  the  widest  and  most  familiar  induction  of 
Biology,  is  that  organisms  grow.  While,  however,  this  is  a 
characteristic  so  habitually  and  markedly  displayed  by  plants 
and  animals,  as  to  be  carelessly  thought  peculiar  to  them, 
it  is  really  not  so.  Under  appropriate  conditions,  increase  of 
size  takes  place  in  inorganic  aggregates,  as  well  as  in  organic 
aggregates.  Crystals  grow  ;  and  often  far  more  rapidly  than 
living  bodies.  Where  the  requisite  materials  are  supplied  in 
the  requisite  forms,  growth  may  be  witnessed  in  non-crystal- 
line masses :  instance  the  fungus-like  accumulation  of 
carbon  that  takes  place  on  the  wick  of  an  unsnuffed  candle. 
On  an  immensely  larger  scale,  we  have  growth  in  geologic 
formations  :  the  slow  accumulation  of  deposited  sediment  into 
a  stratum,  is  not  distinguishable  from  growth  in  its  widest 
acceptation.  And  if  we  go  back  to  the  genesis  of  celestial 
bodies,  assuming  them  to  have  arisen  by  Evolution,  these, 
too,  must  have  gradually  passed  into  their  concrete  shapes 
through  processes  of  growth.  Growth  is  indeed  a  concomi- 
tant of  Evolution  ;  and  if  Evolution  of  one  kind  or  other  is 
universal,  growth  is  universal— universal,  that  is,  in  the 
6ense  that  all  aggregates  display  it  in  some  way  at  somo 
period. 

The  essential  community  of  nature  between  organic 
growth  and  inorganic  growth,  is,  however,  most  clearly  seea 


108  THE    INDUCTIONS    OF    BIOLOGY. 

on  observing  that  they  both  result  in  the  same  way.  The 
segregation  of  different  kinds  of  detritus  from  each  other,  aa 
well  as  from  the  water  carrying  them,  and  their  aggregation 
into  distinct  strata,  is  but  an  instance  of  a  universal  tend- 
ency towards  the  union  of  like  units  and  the  parting  of  un- 
like units  (First  Principles,  §  123).  The  deposit  of  a  crystal 
from  a  solution,  is  a  differentiation  of  the  previously  mixed 
atoms  ;  and  an  integration  of  one  class  of  atoms  into  a  solid 
body,  and  the  other  class  into  a  liquid  solvent.  Is  not  the 
growth  of  an  organism  a  substantially  similar  process  ? 
Around  a  plant  there  exist  certain  elements  that  are  like 
the  elements  which  form  its  substance ;  and  its  increase  of 
size  is  effected  by  continually  integrating  these  surrounding 
like  elements  with  itself.  Nor  does  the  animal  fundament- 
ally differ  in  this  respect  from  the  plant  or  the  crystal.  Its 
food  is  a  portion  of  the  environing  matter,  that  contains  somo 
compound  atoms  like  some  of  the  compound  atoms  constitut- 
ing its  tissues;  and  either  through  simple  imbibition  or 
through  digestion,  the  animal  eventually  integrates  with  it- 
self, units  like  those  of  which  it  is  built  up,  and  leaves  behind 
the  unlike  units.  To  prevent  misconception,  it  may 

be  well  to  point  out  that  growth,  as  here  defined,  must  be 
distinguished  from  certain  apparent  and  real  augmentations 
of  bulk  which  simulate  it.  Thus,  the  long,  white  potato- 
shoots  thrown  out  in  the  dark,  are  produced  at  the  expense 
of  the  substances  which  the  tuber  contains :  they  illustrato 
not  the  accumulation  of  organic  matter,  but  simply  its  re- 
arrangement. Certain  animal-embryos,  again,  during  their 
early  stages,  increase  considerably  in  size  without  assimil- 
ating any  solids  from  the  environment;  and  they  do  this 
by  absorbing  the  surrounding  water.  Even  in  the  highest 
organisms,  as  in  children,  there  appears  sometimes  to  occur 
a  rapid  gain  in  dimensions,  that  does  not  truly  measure  the 
added  quantity  of  organic  matter ;  but  is  in  part  due  to 
ehauges  analogous  to  those  just  named.    Alterations  of  this 


GROWTH.  109 

kind  must  not  be  confounded  with  that  growth,  properly  so 
called,  of  which  we  have  here  to  treat. 

The  next  general  fact  to  be  noted  respecting  organic 
growth,  is,  that  it  has  limits.  Here  there  appears  to  be  a 
distinction  between  organic  and  inorganic  growth  ;  but  this 
distinction  is  by  no  means  definite.  Though  that  aggreoa- 
tion  of  inanimate  matter  which  simple  attraction  produces, 
may  go  on  without  end  ;  yet  there  appears  to  be  an  end  to 
that  more  definite  kind  of  aggregation  which  results  from 
polar  attraction.  Different  elements  and  compounds,  habitu- 
ally form  crystals  more  or  less  unlike  in  their  sizes  ;  and  each 
seems  to  have  a  size  that  is  not  usually  exceeded  without  a 
tendency  arising  to  form  new  crystals  rather  than  to  increase 
the  old.  On  looking  at  the  organic  kingdom  as  a 

whole,  we  see  that  the  limits  between  which  growth  ranges, 
are  very  wide  apart.     At  the  one  extreme,  we  have  monads 
bo  minute  as  to  be  rendered  but  imperfectly  visible  by  micro- 
scopes of  the  highest  power ;  and  at  the  other  extreme,  we 
have  trees  of  300  feet  high,  and  animals  of  100  feet  long. 
It  is  true  that  though  in  one  sense  this  contrast  may  be 
legitimately  drawn,  yet  in  another  sense  it  may  not ;  since 
these  largest  organisms  are  made  by  the  combination  of  units 
that  are  individually  like  the  smallest.     A  single  plant  of  the 
genus  Protococcus,  is  of  the  same  structure  as  one  of  the 
many  cells  united  together  to   form   the   thallus   of  some 
higher  Alga,  or  the  leaf  of  a  phgenogam.     Each  separate 
6hoot    of    a    phaenogam    is    usually    the    bearer   of    many 
leaves.     And  a  tree  is  an  assemblage  of  numerous  united 
shoots.      One   of  these   great   teleophytes   is   thus   an  ag- 
gregate of  aggregates  of  aggregates  of  units,  which  sever- 
ally  resemble  protophytes    in   their   sizes  and   structures; 
and  a  like  building  up  is  traceable  throughout  a  consider- 
able part  of  the  animal  kingdom.     Even,  however,   when 
we  bear  in   mind   this    qualification,   and   make   our   com- 
parisons between  organisms  of  the  same  degree  of  compo 


110  THE    INDUCTIONS    OF    BIOLOGY. 

sition,  we  still  find  the  limit  of  growth  to  have  a  great 
range.  The  smallest  branched  flowering  plant  is  extremely 
insignificant  by  the  side  of  a  forest  tree;  and  there  is  an 
enormous  difference  in  bulk  between  the  least  and  the  great- 
est mammal.  But  on  comparing  members  of  the  same 
species,  we  discover  the  limit  of  growth  to  be  much  less  vari- 
able. Among  the  Protozoa  and  Protophyta,  each  kind  has  a 
tolerably  constant  adult  size ;  and  among  the  most  complex 
organisms,  the  differences  between  those  of  the  same  kind 
that  have  reached  maturity,  are  usually  not  very  great. 
The  compound  plants  do,  indeed,  sometimes  present  marked 
contrasts  between  stunted  and  well-grown  individuals ;  but 
the  higher  animals  diverge  but  inconsiderably  from  the 
average  standards  of  their  species. 

On  surveying  the  facts  with  a  view  of  empirically  general- 
izing the  causes  of  these  differences,  we  are  soon  made  aware 
that  by  variously  combining  and  conflicting  with  each  other, 
these  causes  produce  great  irregularities  of  result.  It  be- 
comes manifest  that  no  one  of  them  can  be  traced  to  it  a 
consequences,  unqualified  by  the  rest.  Hence  the  several 
statements  contained  in  the  following  paragraphs,  must  be 
taken  as  subject  to  mutual  modification. 

Let  us  consider  first,  the  connexion  between  degree  of 
growth  and  complexity  of  structure.  This  connexion  being 
involved  with  many  others,  becomes  apparent  only  on  so 
averaging  the  comparisons,  as  to  eliminate  differences  among 
the  rest.  Nor  does  it  hold  at  all  where  the  conditions  are 
radically  dissimilar;  as  between  plants  and  animals.  But 
bearing  in  mind  these  qualifications,  we  shall  see  that 
organization  has  a  determining  influence  on  increase  of 
mass.  Of  plants  the  lowest,  classed  as  Thallogens, 

usually  attain  no  considerable  size.  Lichens,  Algoe,  and  Fun- 
gi, count  among  their  numbers  but  few  bulky  species :  the 
largest,  such  as  certain  Algae  found  in  antartic  seas,  not 
serving  greatly  to  raise  the  average.  Though  among 
Acrogens  there  are  some,  as  the  Tree-ferns,  whiuh  attain  a 


GROWTH.  Ill 

considerable  height,  the  majority  are  but  of  humble  growth. 
The  Endogens,  including  at  one  extreme  small  grasses  and 
at  the  other  tall  palms,  show  us  an  average  and  a  maximum 
greater  than  that  reached  by  the  Acrogens.  And  the  En- 
dogens are  exceeded  by  the  Exogens  ;  among  which  are 
found  the  monarchs  of  the  vegetal  kingdom.  Pass- 

ing to  animals,  we  meet  the  fact  that  the  size  attained  by 
Vertebrata  is  usually  much  greater  than  the  size  attained  by 
Invertebrate.  Of  invertebrate  animals  the  smallest,  classed 
as  Protozoa,  are  also  the  simplest ;  and  the  largest,  be- 
longing to  the  Annulosa  and  Mollusca,  are  among  the  most 
complex  of  their  respective  types.  Of  vertebrate  animals 
we  see  that  the  greatest  are  Mammals  ;  and  that  though, 
in  past  epochs,  there  were  reptiles  of  vast  bulk,  their  bulk 
did  not  equal  that  of  the  whale.  Between  reptiles  and 
birds,  and  between  land -vertebrates  and  aquatic  vertebrates, 
the  relation  does  not  hold  :  the  conditions  of  existence  be- 
ing in  these  cases  widely  different.  But  among  fishes  as  a 
class,  and  among  reptiles  as  a  class,  it  is  observable  that, 
speaking  generally,  the  larger  species  are  framed  on  the 
higher  types.  The  critical  reader,  who  has  men- 

tally checked  these  statements  in  passing  them,  has  doubtless 
already  seen  that  this  relation  is  not  a  dependence  of  or- 
ganization on  growth,  but  a  dependence  of  growth  on  or- 
ganization. The  majority  of  Exogens  are  smaller  than  some 
Endogens ;  many  Endogens  are  exceeded  in  size  by  certain 
Acrogens ;  and  even  among  Thallogens,  the  least  developed 
of  plants,  there  are  kinds  of  a  size  which  many  plants  of  the 
highest  order  do  not  reach.  Similai-ly  among  animals : 
there  are  plenty  of  Crustaceans  less  than  Actiniae ;  numerous 
reptiles  are  smaller  than  some  fish;  the  majority  of  mam- 
mals are  inferior  in  bulk  to  the  largest  reptiles ;  and  in  the 
contrast  between  a  mouse  and  a  well-grown  Medusa,  we  see  a 
creature  that  is  elevated  in  the  scale  of  organization,  ex- 
ceeded in  mass  by  one  that  is  extremely  degraded.  Clearly 
then,  it  cannot  be  held  that  high  organization  is  habitually 


112  THE    INDUCTIONS    OF    BIOLOGY. 

accompanied  by  great  size.  The  proposition  here  illustrated 
is  the  converse  one,  that  great  size  is  habitually  accompanied 
by  high  organization.  The  conspicuous  fact  that  the  largest 
species  of  both  animals  and  vegetals  belong  to  the  highest 
classes ;  and  that  throughout  their  various  sub-classes  the 
higher  usually  contain  the  more  bulky  forms  ;  shows  this 
connexion  as  clearly  as  we  can  expect  it  to  be  shown,  amid 
so  many  modifying  causes  and  conditions. 

The  relation  between  growth  and  supply  of  available 
nutriment,  is  too  familiar  a  relation  to  need  proving.  There 
are,  however,  some  aspects  of  it  that  must  be  contemplated  be- 
fore its  implications  can  be  fully  appreciated.  Among 
plants,  which  are  all  constantly  in  contact  with  the  gaseous, 
liquid,  and  solid  matters  to  be  incorporated  with  their  tissues  ; 
and  which,  in  the  same  locality,  receive  not  very  unlike 
amounts  of  light  and  heat ;  differences  in  the  supplies  of 
available  nutriment,  have  but  a  subordinate  connexion  with 
differences  of  growth.  Though  in  a  cluster  of  herbs  spring- 
ing up  from  the  seeds  let  fall  by  a  parent,  the  greater  size  of 
some  than  of  others  is  doubtless  due  to  better  nutrition, 
consequent  on  accidental  advantages  ;  yet  no  such  inter- 
pretation can  be  given  of  the  contrast  in  size  between  these 
herbs  and  an  adjacent  tree.  Other  conditions  here  come  into 
play  :  one  of  the  most  important  probably  being,  an  absence  in 
the  one  case,  and  presence  in  the  other,  of  an  ability  to  se- 
crete such  a  quantity  of  ligneous  fibre  as  will  produce  a  stem 
capable  of  supporting  a  large  growth.  Among 
animals,  however,  which  (excepting  some  Entozoa)  differ 
from  plants  in  this,  that  instead  of  bathing  their  surfaces, 
the  matters  they  subsist  on  are  dispersed,  and  have  to  be 
obtained ;  the  relation  between  available  food  and  growth, 
is  shown  with  more  regularity.  The  Protozoa,  living  on 
microscopic  fragments  of  organic  matter  contained  in  the 
surrounding  water,  are  unable,  during  their  brief  lives,  to 
accumulate  any  considerable  quantity  of  nutriment.  Polypes 
and  Mollmcoida,  having  for  food  these  scarcely  visible  mem- 


GROWTH.  1 18 

bers  of  the  animal  kingdom,  are,  though  large  compared 
with  their  prey,  small  as  measured  by  other  standards  :  even 
when  aggregated  into  groups  of  many  individuals,  which 
severally  catch  food  for  the  common  weal,  they  are  often  so 
inconspicuous  as  readily  to  be  passed  over  by  the  unobservant. 
And  if  from  this  point  upwards  we  survey  the  successive 
grades  of  animals,  it  becomes  manifest  that,  in  proportion  aa 
the  size  is  great,  the  masses  of  nutriment  are  either  large,  or, 
what  is  practically  the  same  thing,  are  so  abundant  and  so 
grouped  as  that  large  quantities  may  be  readily  taken  in. 
Though,  for  example,  the  greatest  of  mammals,  the  arctic 
whale,  feeds  on  such  comparatively  small  creatures  as  the 
acalephes  and  molluscs  floating  in  the  seas  it  inhabits,  its 
method  of  gulping  in  whole  shoals  of  them  and  filtering 
away  the  accompanjung  water,  enables  it  to  secure  great 
quantities  of  food.  We  may  then  with  safety  say,  that, 
other  things  equal,  the  growth  of  an  animal  depends  on  the 
abundance  and  sizes  of  the  masses  of  nutriment  which  its 
powers  enable  it  to  appropriate.  Perhaps  it  may  be 

needful  to  add  that,  in  interpreting  this  statement,  the 
number  of  competitors  must  be  taken  into  account.  Clearly, 
not  the  absolute,  but  the  relative,  abundance  of  fit  food  is 
the  point ;  and  this  relative  abundance  very  much  depends 
on  how  many  individuals  are  competing  for  the  food.  Thus 
all  who  have  had  experience  of  fishing  in  Highland  lochs, 
know  that  where  the  trout  are  numerous  they  are  small,  and 
that  where  they  are  comparatively  large  they  are  compara- 
tively few. 

What  is  the  relation  between  growth  and  expenditure  cf 
force  ?  is  a  question  which  next  presents  itself.  Though 
there  is  reason  to  believe  such  a  relation  exists,  it  is  not  very 
readily  traced  :  involved  as  it  is  with  so  many  other  rela- 
tions. Some  contrasts,  however,  ma)T  be  pointed  out,  that 
appear  to  give  evidence  of  it.  Passing  over  the  vegetal 
kingdom,  throughout  which  the  expenditure  of  force  is  too 
small  to  allow  of  such  a  relation  being  visible ;  let  us  seek  in 


114  THE    INDUCTIONS   OF    BIOLOGY. 

the  animal  kingdom,  some  case  where  classes  otherwise 
allied,  are  contrasted  in  their  locomotive  activities.  Let  us 
compare  birds  on  the  one  hand,  with  reptiles  and  mammals 
3n  the  other.  It  is  an  accepted  doctrine  that  birds  are 
organized  on  a  type  closely  allied  to  the  reptilian  type,  but 
superior  to  it ;  and  though  in  many  respects  the  organization 
of  birds  is  inferior  to  that  of  mammals,  yet  in  other  respects, 
as  in  the  greater  heterogeneity  and  integration  of  the  skeleton, 
the  more  complex  development  of  the  respiratory  system, 
and  the  higher  temperature  of  the  blood,  it  may  be  held 
that  birds  stand  above  mammals.  Hence  were  growth  de- 
pendent only  on  organization,  we  might  infer  that  the  limit 
of  growth  among  birds  should  not  be  much  short  of  that 
among  mammals  ;  and  that  the  bird-type  should  admit  of  a 
larger  growth  than  the  reptile-type.  Again,  we  see  no  mani- 
fest disadvantages  under  which  birds  labour  in  obtaining 
food,  but  from  which  reptiles  and  mammals  are  free.  On  the 
contrary,  birds  are  able  to  get  at  food  that  is  fixed  beyond 
the  reach  of  reptiles  and  mammals  ;  and  can  catch  food  that 
is  too  swift  of  movement  to  be  ordinarily  caught  by  reptiles 
and  mammals.  Nevertheless,  the  limit  of  growth  in  birds, 
falls  far  below  that  reached  by  reptiles  and  mammals.  With 
what  other  contrast  between  these  classes,  is  this  contrast 
connected  ?  May  we  not  suspect  that  it  is  connected  with 
the  contrast  between  their  amounts  of  locomotive  exertion  ? 
"Whereas  mammals  (excepting  bats,  which  are  small),  are 
during  all  their  movements  supported  by  solid  surfaces  or 
dense  liquids ;  and  whereas  reptiles  (excepting  the  ancient 
pterodactyles,  which  were  not  very  large),  are  similarly  re- 
stricted in  their  spheres  of  movement ;  the  majority  of  birds 
move  more  or  less  habitually  through  a  rare  medium,  in  which 
they  cannot  support  themselves  without  relatively  great 
efforts.  The  conclusion  that  there  exists  this  inverse 

ratio  between  growth  and  expenditure  of  force,  is  enforced 
by  the  significant  fact,  that  those  members  of  the  class  Aves, 
as  the  Dinornis  and  Ejiiornis,  which  approached  in  size  to 


GROWTH.  115 

the  larger  Mammalia  and  Rcptilia,  wore  creatures  incapable 
of  flight — creatures  which  did  not  expend  this  excess  of 
force  in  locomotion.  Further  evidence  that  there  is 

an  antagonism  between  the  increase  of  bulk  and  the  quantity 
of  motion  evolved  by  an  organism,  is  supplied  by  the  ge- 
neral experience,  that  human  beings  and  domestic  animals, 
when  overworked  while  growing,  are  prevented  from  attain- 
ing the  ordinary  dimensions. 

One  other  general  truth  concerning  degrees  of  growth, 
must  be  set  down.  It  is  a  rule,  having  exceptions  of  no 
great  importance,  that  large  organisms  commence  their 
separate  existences  as  masses  of  organic  matter  more  or  less 
considerable  in  size,  and  commonly  with  organizations  more  or 
less  advanced;  and  that  throughout  each  organic  sub-kingdom, 
there  is  a  certain  general,  though  irregular,  relation  between 
the  initial  and  the  final  bulks.  Yegetals  exhibit  this 

relation  much  less  clearly  and  constantly  than  animals.  Yet 
though,  among  the  plants  that  begin  life  as  minute  spores, 
there  are  some  which,  under  their  special  conditions,  grow  to 
considerable  sizes,  the  immense  majority  of  them  remain 
small.  While,  conversely,  the  great  Endogens  and  Exogens, 
when  thrown  off  from  their  parents,  have  already  the  formed 
organs  of  young  plants,  to  which  are  attached  large  stores  of 
highly  nutritive  matter.  That  is  to  say,  where  the  young 
plant  consists  merely  of  a  centre  of  development,  the  ultimate 
growth  is  commonly  insignificant ;  but  where  the  growth 
is  to  become  great,  there  exists  to  start  with,  a  well-developed 
embryo  and  a  stock  of  assimilable  matter.  Through- 

out the  animal  kingdom,  this  relation  is  tolerably  regular. 
Save  among  classes  that  escape  the  ordinary  requirements  of 
animal  life,  small  germs  or  eggs  do  not  give  rise  to  bulky 
creatures.  Where  great  bulk  is  to  be  reached,  the  young 
proceeds  from  an  egg  of  considerable  bulk,  or  is  born  of  con- 
siderable bulk  ready-organized  and  partially  active.  In  the 
class  fishes,  for  instance,  a  certain  average  proportion  obtains 
between  the  sizes  of  the  ova  and  the  sizes  of  the  adult  indi 


116 


THE    INDUCTIONS   OF    BIOLOGT. 


dividuals  ;  and  among  the  highest  fishes,  as  sharks,  the 
eggs  are  comparatively  few  and  comparatively  large.  Rep- 
tiles ha^e  eggs  that  are  smaller  in  number,  and  relatively 
greater  in  mass,  than  those  of  fishes  ;  and  throughout  this 
class,  too,  there  is  a  general  ratio  between  the  bulk  of  the  egg 
and  the  bulk  of  the  adult  creature.  As  a  group,  birds  show 
us  a  further  limitation  in  the  number  of  their  eggs,  and  a 
further  increase  in  their  relative  sizes ;  and  from  the  minute 
eggs  of  the  humming-bird  up  to  the  immense  ones  of  the 
Epiomis,  holding  several  quarts,  we  see  that,  speaking  ge- 
nerally, the  greater  the  eggs,  the  greater  the  birds.  Finally, 
among  mammals  (omitting  the  marsupials)  the  young  are 
born,  not  only  of  comparatively  large  sizes,  but  with  ad- 
vanced organizations  ;  and  throughout  this  sub-division  of 
the  vertebrata,  as  throughout  the  others,  there  is  a  mani- 
fest connexion  between  the  sizes  at  birth  and  the  sizes  at 
maturity.  As   having   a   kindred  meaning,   there 

must  finally  be  noted  the  fact,  that  the  young  of  these 
highest  animals,  besides  starting  in  life  with  bodies  of 
considerable  sizes,  almost  fully  organized,  are,  during  sub- 
sequent periods  of  greater  or  less  length,  supplied  with  nutri- 
ment— in  birds  by  feeding,  and  in  mammals  by  suckling  and 
afterwards  by  feeding.  That  is  to  say,  beyond  the  mass  and 
organization  directly  bequeathed,  a  bird  or  mammal  obtains 
a  further  large  mass  at  but  little  cost  to  itself. 

Were  an  exhaustive  treatment  of  the  topic  intended,  it 
would  be  needful  to  give  a  paragraph  to  each  of  the  many 
incidental  circumstances  by  which  growth  may  be  aided  or 
restricted.  Such  facts  as  that  an  entozoon  is  limited  by  the 
size  of  the  creature,  or  even  the  organ,  in  which  it  thrives  ; 
that  an  epizoon,  though  getting  abundant  nutriment  with- 
out appreciable  exertion,  is  restricted  to  that  small  bulk  at 
which  it  escapes  ready  detection  by  the  animal  it  infests  ; 
that  sometimes,  as  in  the  weazel,  smallness  is  a  condition  to 
successful  pursuit  of  the  animals  preyed  upon ;  and  that  at 
other  times,  the  advantage  of  resembling  certain  other  crea- 


GROWTH.  117 

tures,  and  so  deceiving  enemies  or  prey,  becomes  an  indirect 
cause  of  restricted  size.  But  the  present  purpose  is  simply 
to  set  down  those  most  general  relations  between  growth  and 
other  organic  phenomena,  which  induction  leads  us  to. 
Having  done  this,  let  us  go  on  to  inquire  whether  these 
general  relations  can  be  deductively  established. 

§  4-1.  That  there  must  exist  a  certain  dependence  of 
growth  on  organization,  may  be  shown  a  priori.  When  we 
consider  the  phenomena  of  Life,  either  by  themselves  or  in 
their  relations  to  surrounding  phenomena,  we  see  that,  other 
things  equal,  the  larger  the  aggregate  the  greater  is  the 
needful  complexity  of  structure. 

In  plants,  even  of  the  highest  type,  there  is  a  com- 
paratively small  mutual  dependence  of  parts  :  a  gathered 
flower-bud  will  unfold  and  flourish  for  days,  if  its  stem  be 
immersed  in  water  ;  and  a  shoot  cut  off  from  its  parent-tree 
and  stuck  in  the  ground,  will  grow.  The  respective  parts 
having  vital  activities  that  are  not  widely  unlike,  it  is  pos- 
sible for  great  bulk  to  be  reached  without  that  structural 
complexity  required  for  combining  the  actions  of  parts. 
Even  here,  however,  we  see  that  for  the  attainment  of  great 
bulk,  there  requires  such  a  degree  of  organization  as  shall 
co-ordinate  the  functions  of  roots  and  branches — we  see 
that  such  a  size  as  is  reached  by  trees,  is  not  possible 
without  an  efficient  vascular  system  enabling  the  remote 
organs  to  utilize  each  other's  products.  And  we  see  that 
such  a  co-existence  of  large  growth  with  low  organization, 
as  occurs  in  seme  of  the  marine  Algce,  occurs  where  the 
conditions  of  existence  do  not  necessitate  any  considerable 
mutual  dependence  of  parts — where  the  near  approach  of  the- 
plant  to  its  medium  in  specific  gravity,  precludes  the  need  of 
a  well -developed  stem,  and  where  all  the  materials  of  growth 
being  derived  from  the  water  by  each  portion  of  the  thallus, 
there  requires  no  apparatus  for  transferring  materials  from 
port  to  part.  Among  animals  which,  with  but  few 


118 


THE    INDUCTIONS   OF    BIOLOOr. 


exceptions,  are,  by  the  conditions  of  their  existence,  required 
to  take  in  nutriment  through  one  specialized  part  of  the 
body,  it  is  clear  that  there  must  be  a  means  whereby  other 
parts  of  the  body,  to  be  supported  by  this  nutriment,  must 
have  it  conveyed  to  them.  It  is  clear  that  for  an  equally 
efficient  maintenance  of  their  nutrition,  the  parts  of  a  larg6 
mass  must  have  a  more  elaborate  propelling  and  conducting 
apparatus ;  and  that  in  proportion  as  these  parts  undergo 
greater  waste,  a  yet  higher  development  of  the  vascular 
system  is  necessitated.  Similarly  with  the  pre-requisites  to 
those  mechanical  motions  which  animals  are  required  to 
perform.  The  parts  of  a  mass  cannot  be  made  to  move,  and 
have  their  movements  so  co-ordinated  as  to  produce  locomo- 
tive and  other  actions,  without  certain  structural  arrange- 
ments ;  and,  other  things  equal,  a  given  amount  of  such 
activity  requires  more  involved  structural  arrangements  in  a 
large  mass  than  in  a  small  one.  There  must  at  least  be  a 
co-ordinating  apparatus  presenting  greater  contrasts  in  its 
central  and  peripheral  parts. 

The  qualified  dependence  of  growth  on  organization,  is 
equally  implied  when  we  study  it  in  Connexion  with  that 
adjustment  of  inner  to  outer  relations  which  constitutes  Life. 
In  plants  this  is  not  conspicuous,  because  the  adjustment  of 
inner  to  outer  relations  is  but  small.  Still,  it  is  visible  in  tie 
fact  that  the  condition  on  which  only  a  plant  can  grow  to  a 
great  size,  is,  that  it  shall,  by  the  development  of  a  massive 
trunk,  present  inner  relations  of  forces  fitted  to  counter- 
balance those  outer  relations  of  forces,  which  tend  continually 
and  occasionally  to  overthrow  it ;  and  this  formation  of  a 
core  of  regularly- arranged  woody  fibres,  is  an  advance  in 
organization.  Throughout  the  animal  kingdom,  this 

connexion  of  phenomena  is  manifest.  To  obtain  materials  for 
growth  ;  to  avoid  injuries,  which  interfere  with  growth ;  and 
to  escape  those  enemies  which  bring  growth  to  a  sudden  end  ; 
implies  in  the  organism,  the  means  of  fitting  its  movements 
to  meet   numerous  external  co-existences  and  sequences — 


GROWTH.  119 

implies  such  various  structural  arrangements  as  shall  make 
possible  these  variously-adapted  actions.  It  cannot  be 
questioned  that,  everything  else  remaining  constant,  a  more 
complex  animal,  capable  of  adjusting  its  conduct  to  a  greater 
number  of  surrounding  contingences,  will  be  the  better  able 
to  secure  food  and  evade  damage,  and  so  to  increase  bulk. 
And  evidently,  without  any  qualification,  we  may  say  that  a 
large  animal,  living  under  such  complex  conditions  of  exist- 
ence as  everywhere  obtain,  is  not  possible  without  compara- 
tively high  organization. 

While,  then,  this  relation  is  traversed  and  obscured  by 
sundry  other  relations,  it  cannot  but  exist.  Deductively  we 
see  that  it  must  be  modified,  as  inductively  we  saw  that  it  is 
modified,  by  the  circumstances  amid  which  each  kind  of  or- 
ganism is  placed ;  but  that  it  is  always  a  factor  in  determin- 
ing the  result. 

§  45.  That  growth  is,  ceeteris paribus,  dependent  on  the  sup- 
ply of  assimilable  matter,  is  a  proposition  so  continually  illus- 
trated by  special  experience,  as  well  as  so  obvious  from  general 
experience,  that  it  would  scarcely  need  stating,  were  it  not  re- 
quisite to  notice  the  qualifications  with  which  it  must  be  taken. 

The  materials  which  each  organism  requires  for  building 
itself  up,  are  not  of  one  kind,  but  of  several  kinds.  As  a 
vehicle  for  transferring  matter  through  their  structures,  all 
organisms  require  water  as  well  as  solid  constituents ;  and  how- 
ever abundant  the  solid  constituents,  there  can  be  no  growth 
in  the  absence  of  water.  Among  the  solids  supplied,  there 
must  be  a  proportion  ranging  within  certain  limits.  A 
plant  round  which  carbonic  acid,  water,  and  ammonia  exist 
in  the  right  quantities,  may  yet  be  arrested  in  its  growth  by 
a  deficiency  of  silica.  The  total  absence  of  lime  from  its 
food,  may  stop  the  formation  of  a  mammal's  skeleton  :  thus 
dwarfing,  if  not  eventually  destroying,  the  mammal ;  and 
this,  no  matter  what  quantities  of  other  needful  colloids  and 
crystalloids  are  furnished. 


120  THE    INDUCTIONS   OF    BIOLOGY. 

Again,  the  truth  that,  other  things  equal,  growth  varic3 
according  to  the  supply  of  nutriment,  has  to  be  qualified  by 
the  condition,  that  the  supply  shall  not  exceed  the  ability  to 
appropriate  it.  In  the  vegetal  kingdom,  the  assimilating 
surface  being  external,  and  admitting  of  rapid  expansion  by 
the  formation  of  new  roots,  shoots,  and  leaves,  the  effect  of 
this  limitation  is  not  conspicuous  :  by  artificially  supplying 
plants  with  those  materials  which  they  have  usually  the  most 
difficulty  in  obtaining,  we  can  greatly  facilitate  their  growth ; 
and  so  can  produce  striking  differences  of  size  in  the  same 
species.  Even  here,  however,  the  effect  is  confined  within 
the  limits  of  the  ability  to  appropriate ;  since  in  the  absence 
of  that  solar  light  and  heat,  by  the  help  of  which  the  chief 
appropriation  is  carried  on,  the  additional  materials  of 
growth  are  useless.  In  the  animal  kingdom  this 

restriction  is  rigorous.  The  absorbent  surface  being,  in  the 
great  majority  of  cases,  internal ;  having  a  comparatively 
small  area,  which  cannot  be  greatly  enlarged  without  re- 
construction of  the  whole  body  ;  and  being  in  connexion 
with  a  vascular  system,  which  must  also  be  re-constructed 
before  any  considerable  increase  of  nutriment  can  be  made 
available  ;  it  is  clear  that  beyond  a  certain  point,  very  soon 
reached,  increase  of  nutriment  will  not  cause  increase  of 
growth.  On  the  contrary,  if  the  quantity  of  nutriment 
taken  in,  is  greatly  beyond  the  absorbent  power,  the  excess, 
becoming  an  obstacle  to  the  regular  working  of  the  organism, 
may  retard  growth  rather  than  advance  it. 

While  then  it  is  certain,  a  priori,  that  there  cannot  be 
growth  in  the  absence  of  such  substances  as  those  of  which 
an  organism  consists ;  and  while  it  is  equally  certain  that  the 
amount  of  growth  must  primarily  be  governed  by  the  supply 
of  these  substances ;  it  is  not  less  certain  that  extra  supply 
will  not  produce  extra  growth,  beyond  a  point  very  soon 
reached.  Deduction  shows  to  be  necessary,  as  induction 
makes  familiar,  the  truths  that,  the  value  of  food  for  purposes 
of    growth    depends   not   on   the   quantity   of    the   various 


GROWTH. 


121 


organizable  materials  it  contains,  but  on  the  quantity  of 
the  material  most  needed  ;  that  given  a  right  proportion  of 
materials,  the  pre-existing  structure  of  the  organism  limits 
their  availability  ;  and  that  the  higher  the  structure,  the 
sooner  is  this  limit  reached. 

§  46.  But  why  should  the  growth  of  every  organism  be 
finally  arrested  ?  Though  the  rate  of  increase  may,  in  each 
case,  be  necessarily  restricted  within  a  narrow  range  of  varia- 
tion— though  the  increment  that  is  possible  in  a  given  time, 
cannot  exceed  a  certain  amount ;  yet  why  should  the  incre- 
ments decrease,  and  finally  become  insensible  ?  Why  should 
not  all  organisms,  when  supplied  with  sufficient  materials, 
continue  to  grow  as  long  as  they  live  ?  To  find  an  answer 
to  this  question,  we  must  first  revert  to  the  nature  and 
functions  of  organic  matter. 

In  the  first  three  chapters  of  Part  I.,  it  was  shown  that 
plants  and  animals  mainly  consist  of  substances  in  states  of 
unstable  equilibrium — substances  which  have  been  raised  to 
this  unstable  equilibrium  by  the  expenditure  of  the  forces  we 
know  as  solar  radiations,  and  which  give  out  these  forces  in 
other  forms,  on  falling  into  states  of  stable  equilibrium. 
Leaving  out  the  water,  which  serves  as  a  vehicle  for  these 
materials  and  a  medium  for  their  changes ;  and  excluding 
those  mineral  matters  that  play  either  passive  or  subsidiary 
parts  ;  organisms  are  built  up  of  compounds  which  are  stores 
of  force.  Those  complex  colloids  and  crystalloids  which,  as 
united  together,  form  organized  bodies,  are  the  same  colloids 
and  crystalloids  which  give  out,  on  their  decomposition,  the 
forces  expended  by  organized  bodies.  Thus  these 

nitrogeneous  and  carbonaceous  substances,  being  at  once 
the  materials  for  organic  growth  and  the  sources  of  organic 
force  ;  it  results  that  as  much  of  them  as  is  used  up  for  the 
genesis  of  force,  is  taken  away  from  the  means  of  growth ; 
and  as  much  as  is  economized  by  diminishing  the  genesis  of 
force,  is  available  for  growth.  Given  that  limited  quantity 
9 


122  1HE    INDUCTIONS    OF    BIOLOGY. 

of  nutritive  matter  which  the  pre-existing  structure  of  nz\ 
organism  enables  it  to  absorb  ;  and  it  is  a  necessary  corollary 
from  the  persistence  of  force,  that  the  matter  accumulated  as 
growth,  cannot  exceed  that  surplus  which  remains  unde- 
composed,  after  the  production  of  the  required  amounts  ol 
sensible  and  insensible  motion.  This,  which  would 

be  rigorously  true  under  all  conditions,  if  exactly  the  sams 
substances  were  used  in  exactly  the  same  proportions,  for  the 
production  of  force  and  for  the  formation  of  tissue,  requires, 
however,  to  be  taken  with  the  qualification,  that  some  of  the 
force-evolving  substances  are  not  constituents  of  tissue  ;  and 
that  thus,  there  may  be  a  genesis  of  force  which  is  not  at  the 
expense  of  potential  growth.  But  since  organisms  (or  at 
least  animal  organisms,  with  which  we  are  here  chiefly 
concerned,)  have  a  certain  power  of  selective  absorption, 
which,  partially  in  an  individual  and  more  completely  in  a 
race,  adapts  the  proportions  of  the  substances  absorbed  to  the 
needs  of  the  system ;  then  if  a  certain  habitual  expenditure 
of  force,  leads  to  a  certain  habitual  absorption  of  force- 
evolving  matters  that  are  not  available  for  growth  ;  and  if, 
were  there  less  need  for  such  matters,  the  ability  to  absorb 
matters  available  for  growth  would  be  increased  to  an  equi- 
valent extent ;  it  follows  that  the  antagonism  described,  does, 
m  the  long  run,  hold  even  without  this  qualification.  Hence, 
growth  is  substantially  equivalent  to  the  absorbed  nutriment, 
minus  the  nutriment  used  up  in  action. 

This,  however,  is  no  answer  to  the  question — why  has 
individual  growth  a  limit  ?  The  antagonism  described,  does 
not  manifestly  account  for  the  fact,  that  in  every  domestic 
animal  the  increments  of  growth  bear  continually  decreasing 
ratios  to  the  mass,  and  finally  come  to  an  end.  Nevertheless, 
it  is  demonstrable  that  the  excess  of  absorbed  over  expended 
nutriment,  must,  other  things  equal,  become  less  as  the  size  of 
the  animal  becomes  greater.  In  similarly-shaped  bodies, 

the  masses  vary  as  the  cubes  of  the  dimensions  ;  whereas  the 
strengths  vary  as  the  squares  of  the  dimensions.     See  here 


gho-vvth.  123 

the  solution  of  the  problem.  Supposing  a  creature  which  a 
year  ago  was  one  foot  high,  has  now  become  two  feet  high, 
while  it  is  unchanged  in  proportions  and  structure  ;  what  are 
the  necessary  concomitant  changes  that  have  taken  place  in 
it  ?  It  is  eight  times  as  heavy  ;  that  is  to  say,  it  has  to  re- 
sist eight  times  the  strain  which  gravitation  puts  on  its 
structure  ;  and  in  producing,  as  well  as  in  arresting,  every 
one  of  its  movements,  it  has  to  overcome  eight  times  the 
inertia.  Meanwhile,  the  muscles  and.  bones  have  sever- 
ally increased  their  contractile  and  resisting  powers  in  pro- 
portion to  the  areas  of  their  transverse  sections ;  and  hence 
are  severally  but  four  times  as  strong  as  they  were.  Thus, 
while  the  creature  has  doubled  in  height,  and  while  its  ability 
to  overcome  forces  has  quadrupled,  the  forces  it  has  to  overcome 
have  grown  eight  times  as  great.  Hence,  to  raise  its  body 
through  a  given  space,  its  muscles  have  to  be  contracted  with 
twice  the  intensity,  at  a  double  cost  of  matter  expended.  This 
necessity  will  be  seen  still  more  clearly  if  we  leave  out  the 
motor  apparatus,  and  consider  only  the  forces  required  and 
the  means  of  supplying  them.  For  since,  in  similar  bodies, 
the  areas  vary  as  the  squares  of  the  dimensions,  and  the 
masses  vary  as  the  cubes  ;  it  follows  that  the  absorbing  sur- 
face has  become  four  times  as  great,  while  the  weight  to  be 
moved  by  the  matter  absorbed  has  become  eight  times  as 
great.  If  then,  a  year  ago,  the  absorbing  surface  could  take 
up  twice  as  much  nutriment  as  was  needed  for  expenditure, 
thus  leaving  one-half  for  growth,  it  is  now  able  only  just  to 
meet  expenditure,  and  can  provide  nothing  for  growth.  How- 
ever great  the  excess  of  assimilation  over  waste,  may  be  dur- 
ing the  early  life  of  an  active  organism,  we  see  that  because 
a  series  of  numbers  increasing  as  the  cubes,  overtakes  a  series 
increasing  as  the  squares,  even  though  starting  from  a  much 
smaller  number,  there  must  be  reached,  if  the  organism  lives 
long  enough,  a  point  at  which  the  surplus  assimilation  is 
brought  down  to  nothing — a  point  at  which  expenditure  ba- 
lances nutrition — a  state  of  moving  equilibrium.  This. 


124  THE    INDUCTIONS   OF    BIOLOGY. 

however,  though  the  chief,  is  not  the  sole,  varying  relation  be- 
tween degrees  of  growth  and  amounts  of  expended  force.  There 
are  two  more ;  one  of  which  conspires  with  the  last,  while 
the  other  conflicts  with  it.  Consider  in  the  first  place,  the 
cost  at  which  nutriment  is  distributed  through  the  body,  and 
effete  matters  removed  from  it.  Each  increment  of  growth 
being  added  at  the  periphery  of  the  organism,  the  force  ex- 
pended in  the  transfer  of  matter  must  increase  in  a  rapid 
progression — a  progression  more  rapid  than  that  of  the  mass. 
Bat  as  the  dynamic  expense  of  distribution  is  small  compared 
with  the  dynamic  value  of  the  materials  distributed,  this  item 
in  the  calculation  is  unimportant.  Now  consider,  in  the 
second  place,  the  changing  proportion  between  production 
and  loss  of  heat.  In  similar  organisms,  the  quantities  of  heat 
generated  by  similar  actions  going  on  throughout  their  sub- 
stance, must  increase  as  the  masses,  or  as  the  cubes  of  the 
dimensions.  Meanwhile,  the  surfaces  from  which  loss  of  heat 
by  radiation  takes  place,  increase  only  as  the  squares  of  the 
dimensions.  Though  the  loss  of  heat  does  not  therefore  in- 
crease only  as  the  squares  of  the  dimensions,  it  certainly  in- 
creases at  a  smaller  rate  than  the  cubes.  And  to  the  extent 
that  augmentation  of  mass  results  in  a  greater  retention  of 
heat,  it  effects  an  economization  of  force.  This  advantage  is 
not,  however,  so  important  as  at  first  appears.  Organic  heat 
is  a  concomitant  of  organic  action,  and  is  so  abundantly  pro- 
duced during  action,  that  the  loss  of  it  is  then  of  no  conse- 
quence :  indeed  the  loss  is  often  not  rapid  enough  to  keep 
the  supply  from  rising  to  an  inconvenient  excess.  It  is  only 
in  respect  of  that  maintenance  of  heat  which  is  needful  during 
quiescence,  that  large  organisms  have  an  advantage  over 
email  ones  in  this  relatively  diminished  loss.  Thus  these  two 
(subsidiary  relations  between  degrees  of  growth  and  amounts 
of  expended  force,  being  in  antagonism  with  each  other,  we 
may  conclude  that  their  differential  result  does  not  greatly 
modify  the  result  of  the  chief  relation  previously  set  forth. 
Any  one  who  proceeds  to  test  this  deduction,  will  find  some 


GROWTH.  126 

seeming  incongruities  between  it  and  certain  facts  inductively 
established.  Lest  these  should  mislead  him,  it  will  be  well 
to  explain  them.  Throughout  the  vegetal  kingdom, 

he  may  remark  that  there  is  no  limit  of  growth  except  what 
death  entails.  Passing  over  a  large  proportion  of  plants 
which  never  exceed  a  comparatively  small  size,  because  they 
wholly  or  partially  die  down  at  the  end  of  the  year ;  and 
pointing  to  trees  that  annually  send  forth  new  shoots,  even 
when  their  trunks  are  hollowed  out  by  decay ;  he  may  ask — 
How  does  growth  happen  here  to  be  unlimited  ?  The  answer 
is,  that  plants  are  only  accumulators  ;  they  are  in  no  apprecia- 
ble degree  expenders.  As  they  do  not  undergo  a  waste  which 
increases  as  the  cubes  of  the  dimensions,  while  assimilation 
increases  as  their  squares ;  there  is  no  reason  why  their 
growth  should  be  arrested  by  the  equilibration  of  assimilation 
and  waste.  Again,  should  he  look  among  animals  for  an 

exact  correspondence  between  the  decreasing  increments  of 
growth  as  ascertained  by  observation  and  as  determined  by  de- 
duction, he  will  not  find  it.  And  there  are  sufficient  reasons 
why  the  correspondence  cannot  be  more  than  approximate. 
Besides  the  fact  above  noted,  that  there  are  other  varying 
relations  which  complicate  the  chief  one,  he  must  bear  in 
mind  that  the  bodies  compared  are  not  truly  similar :  the 
proportions  of  trunk  to  limbs  and  trunk  to  head,  vary  con- 
siderably. The  comparison  is  still  more  seriously  vitiated  by 
the  inconstant  ratio  between  the  constituents  of  which  the 
body  is  composed.  In  the  flesh  of  adult  mammalia,  water 
forms  from  68  to  71  per  cent.,  organic  substance  from  24  to 
28  per  cent.,  and  inorganic  substance  from  3  to  5  per  cent.; 
whereas  in  the  foetal  state,  the  water  amounts  to  87  per  cent., 
and  the  solid  organic  constituents  to  only  1 1  per  cent.  Clearly 
this  change  from  a  state  in  which  the  force- evolving  matter 
forms  one  tenth  of  the  whole,  to  a  state  in  which  it  forms  two 
and  a  half  tenths,  must  greatly  interfere  with  the  parallelism 
between  the  actual  and  the  theoretical  progression.  Yet 

another  difficulty  may  come  under  his  notice.     The  crocodile 


126  THE    INDUCTIONS    OF    BIOLOGY. 

is  said  to  grow  as  long  as  it  lives ;  and  there  appears  reason 
to  think  that  some  predaceous  fishes,  such  as  the  pike,  do 
the  same.  That  these  animals  of  comparatively  high  organ- 
ization, have  no  definite  limits  of  growth,  is,  however,  an  ex- 
ceptional fact  due  to  the  exceptional  non-fulfilment  of  those 
conditions  which  entail  limitation.  What  kind  of  life  does 
a  crocodile  lead  ?  It  is  a  cold-blooded,  or  almost  cold- 
blooded, creature ;  that  is,  it  expends  very  little  for  the  main- 
tenance of  heat.  It  is  habitually  inert:  not  chasing  prey,  but 
lying  in  wait  for  it ;  and  undergoes  considerable  exertion 
only  during  its  occasional  brief  contests  with  prey.  Such 
other  exertion  as  is,  at  intervals,  needful  for  moving  from 
place  to  place,  is  rendered  small  by  the  small  difference 
between  the  animal's  specific  gravity  and  that  of  water. 
Thus  the  crocodile  expends  in  muscular  action,  an  amount  of 
force  that  is  insignificant  compared  with  the  force  commonly 
expended  by  land-animals.  Hence  its  habitual  assimilation 
is  diminished  much  less  than  usual  by  habitual  waste  ;  and 
beginning  with  an  excessive  disproportion  between  the  two, 
it  is  quite  possible  for  the  one  never  quite  to  lose  its  advance 
over  the  other  while  life  continues.  On  looking  closer  into 
such  cases  as  this  and  that  of  the  pike,  which  is  similarly 
cold-blooded,  similarly  lies  in  wait,  and  is  similarly  able  to 
obtain  larger  and  larger  kinds  of  prey  as  it  increases  in  size  ; 
we  discover  a  further  reason  for  this  absence  of  a  definite 
limit.  The  mechanical  causes  necessitating  a  limit,  are  here 
only  partially  in  action.  For  a  creature  living  in  a  medium 
of  nearly  the  same  density  as  its  bod}'',  has  not  constantly  to 
overcome  that  gravitative  force  which  is  the  chief  resistance 
to  be  met  by  terrestrial  animals :  it  has  not  to  expend  for 
this  purpose,  a  muscular  power  that  is  large  at  the  outset,  and 
increases  as  the  cubes  of  its  dimensions.  The  only  force  in- 
creasing as  the  cubes  of  its  dimensions,  which  it  has  thus  to 
overcome,  is  the  inertia  of  its  parts.  The  exceptional  con- 
tinuance of  growth  observed  in  creatures  so  circumstanced,  ia 
therefore  perfectly  explicable. 


GROWTH.  127 

§  47.  Obviously  this  antagonism  between  accumulation  and 
expenditure,  must  be  a  leading  cause  of  the  contrasts  in  size 
between  allied  organisms  that  are  in  many  respects  similarly 
conditioned.  The  life  followed  by  each  kind  of  animal,  is 
one  involving  a  certain  average  amount  of  exertion  for  the 
obtainment  of  a  given  amount  of  nutriment — an  exertion, 
part  of  which  goes  to  the  gathering  or  catching  of  food,  part 
to  the  tearing  and  mastication  of  it,  and  part  to  the  after- 
processes  requisite  for  separating  the  nutritive  atoms — an 
exertion  which  therefore  varies  according  as  the  food  is  abund- 
ant or  scarce,  fixed  or  moving,  according  as  it  is  mechani- 
cally easy  or  difficult  to  deal  with  when  secured,  and  accord- 
ing as  it  is,  or  is  not,  readily  soluble.  Hence,  while  among 
animals  of  the  same  species  having  the  same  mode  of  life, 
there  will  be  a  tolerably  constant  ratio  between  accumulation 
and  expenditure,  and  therefore  a  tolerably  constant  limit  of 
growth  ;  there  is  every  reason  to  expect  that  different  species, 
following  different  modes  of  life,  will  have  unlike  ratios  be- 
tween accumulation  and  expenditure,  and  therefore  unlike 
limits  of  growth. 

Though  the  facts  as  inductively  established,  show  a  general 
harmony  with  this  deduction,  we  cannot  usually  trace  this 
harmony  in  any  specific  way  ;  since  the  conflicting  and  con- 
spiring causes  which  affect  growth  are  so  numerous.  The 
only  contrast  which  seems  fairly  to  the  point,  is  the  before- 
named  one  between  the  vertebrates  which  fly,  and  the  most 
nearly-allied  vertebrates  which  do  not  fly :  the  differences 
in  degrees  of  organization  and  relations  to  food,  being  not  such 
as  seriously  to  affect  the  comparison.  If  it  be  admitted  that 
birds  habitually  expend  more  force  than  mammals  and  rep- 
tiles, then  it  will  follow  a  priori,  that,  other  things  being 
tolerably  equal,  they  should  have  a  lower  limit  of  growth 
than  mammals  and  reptiles ;  and  this  we  know  to  be  the  fact 
a  posteriori. 

§   18.     One  of  the  chief  causes,  if  not  the  chief  cause,  of 


128  THE   INDUCTIONS   OF   BIOLOGY. 

the  differences  between  the  sizes  of  organisms,  has  yet  to  be 
considered.  We  are  introduced  to  it  by  pushing  the  above 
inquiry  a  little  further.  Small  animals  have  been  shown  to 
possess  an  advantage  over  large  ones,  in  the  greater  ratio 
which,  other  things  equal,  assimilation  bears  to  expenditure: 
and  we  have  seen  that  hence,  small  animals  in  becoming 
large  ones,  gradually  lose  that  surplus  of  assimilative  power 
which  they  had,  and  eventually  cannot  assimilate  more  than 
is  required  to  balance  waste.  But  how  come  these  animals 
while  young  and  small,  to  have  surplus  assimilative  powers  ? 
Have  all  animals  equal  surplus  of  assimilative  powers  ? 
And  if  not,  how  far  do  differences  between  the  surpluses  de- 
termine differences  between  the  limits  of  growth?  We 
shall  find  in  the  answers  to  these  questions,  the  interpretation 
of  many  marked  contrasts  in  growth  that  are  not  due  to  any 
of  the  causes  above  assigned.  For  example,  an  ox  immensely 
exceeds  a  sheep  in  mass.  Yet  the  two  live  from  generation 
to  generation  in  the  same  fields,  eat  the  same  grass  and  tur- 
nips, obtain  these  aliments  with  the  same  small  expenditure 
of  force,  and  differ  scarcely  at  all  in  their  degrees  of  organiz- 
ation. Whence  arises,  then,  their  striking  unlikeness  of  bulk  ? 

We  noted  when  studying  the  phenomena  of  growth  in- 
ductively, that  organisms  of  the  larger  and  higher  types,  com- 
mence their  separate  existences,  as  masses  of  organic  matter 
having  tolerable  magnitudes.  Speaking  generally,  we  saw 
that  throughout  each  organic  sub-kingdom,  the  acquire- 
ment of  great  bulk  occurs  only  where  the  incipient  bulk 
and  organization  are  considerable ;  and  that  they  are  the 
more  considerable  in  proportion  to  the  complexity  of  the  life 
which  the  organism  is  to  lead. 

The  deductive  interpretation  of  this  induction  may  best  be 
commenced  by  an  analogy.  A  street  orange- vendor  makes 
but  a  trifling  profit  on  each  transaction ;  and  unless  more 
than  ordinarily  fortunate,  he  is  unable  to  realize  during 
the  day  a  larger  amount  than  will  meet  his  wants  :  leav- 
ing him  to  start  on  the  mcrrow  in  the  same  condition  as 


GROAVTFI.  129 

before.  The  trade  of  the  huxter  in  ounces  of  tea  and  half- 
pounds  of  sugar,  is  one  similarly  entailing  much  labour  for 
small  returns.  Beginning  with  a  capital  of  a  few  pounds,  it 
is  impossible  for  him  to  have  a  shop  large  enough,  or  goods 
sufficiently  abundant  and  various,  to  permit  an  extensive 
business  :  he  must  be  content  with  the  half-pence  and  pence 
which  he  makes  by  little  sales  to  poor  people  ;  and  if,  avoid- 
ing bad  debts,  he  is  able  by  strict  economy  to  accumulate 
anything,  it  can  be  but  a  trifle.  A  large  retail  trader  is 
obliged  to  lay  out  much  money  in  fitting  up  an  adequate 
establishment ;  he  must  invest  a  still  greater  sum  in  stock  ; 
and  he  must  have  a  further  floating  capital  to  meet  the 
charges  that  fall  due  before  his  returns  come  in.  Setting 
out,  however,  with  means  enough  for  these  purposes,  he  is 
able  to  make  numerous  and  comparatively  large  sales ;  and 
so  to  get  greater  and  more  numerous  increments  of  profit. 
Similarly,  to  get  returns  in  thousands,  merchants  and  manu- 
facturers must  make  their  investments  in  tens  of  thousands. 
In  brief,  the  rate  at  which  a  man's  wealth  accumulates,  is 
measured  by  the  surplus  of  income  over  expenditure  ;  and 
this,  save  in  exceptionably  favourable  cases,  is  determined  by 
the  capital  with  which  he  begins  business.  Now  ap- 

plying the  analogy,  we  may  trace  in  the  transactions  of  an 
organism,  the  same  three  ultimate  elements.  There  is  the 
expenditure  required  for  the  obtainment  and  digestion  of 
food ;  there  is  the  gross  return  in  the  shape  of  nutriment  as- 
similated, or  fit  for  assimilation ;  and  there  is  the  difference 
between  this  gross  return  of  nutriment  and  the  nutriment 
that  was  used  up  in  the  labour  of  securing  it — a  difference 
which  may  be  a  profit  or  a  loss.  Clearly,  however,  a  surplus 
implies  that  the  force  expended  is  less  than  the  force  latent 
in  the  assimilated  food.  Clearly,  too,  the  increment  of 
growth  is  limited  to  the  amount  of  this  surplus  of  income 
over  expenditure  ;  so  that  large  growth  implies  both  that  the 
excess  of  nutrition  over  waste  shall  be  relatively  considerable, 
and  that  the  waste  and  nutrition  shall  be  on  extensive  scales. 


130  THE    INDUCTIONS  OF    BIOLOGY. 

And  clearly,  the  ability  of  an  organism  to  expend  largely  and 
assimilate  largely,  so  as  to  make  a  large  surplus,  presupposes 
a  large  physiological  capital,  in  the  shape  of  organic  matter 
more  or  less  complete  in  its  structural  arrangements. 

Throughout  the  vegetal  kingdom,  the  illustrations  of  this 
truth  are  not  conspicuous  and  regular  :  the  obvious  reason 
being,  that  since  plants  are  accumulators  and  in  so  small  a 
degree  expenders,  the  premises  of  the  above  argument  are 
but  very  partially  fulfilled.  The  food  of  plants  (excepting 
Fungi  and  certain  parasites)  being  in  a  great  measure  the 
same  for  all,  and  bathing  all  so  that  it  can  be  absorbed  with- 
out effort,  their  vital  processes  result  almost  entirely  in  profit. 
Once  fairly  rooted  in  a  fit  place,  a  plant  may  thus  from  the 
outset  add  its  entire  returns  to  capital ;  and  may  soon  be  able 
to  carry  on  its  processes  on  a  large  scale,  though  it  does  not 
at  first  do  so.  When,  however,  plants  are  expenders,  namely, 
during  their  germination  and  first  stages  of  growth,  their 
degrees  of  growth  are  determined  by  their  amounts  of  vital 
capital.  It  is  because  the  young  tree  commences  life  with  a 
ready- formed  embryo  and  store  of  food  sufficient  to  last  for 
some  time,  that  it  is  enabled  to  strike  root  and  lift  its  head 
above  the  surrounding   herbage.  Throughout  the 

animal  kingdom,  however,  the  necessity  of  this  relation  is 
everywhere  obvious.  The  small  carnivore  preying  on  small 
herbivores,  can  increase  in  size  only  by  small  increments  :  its 
organization  unfitting  it  to  digest  larger  creatures,  even  if  it 
ran  kill  them,  it  cannot  profit  by  amounts  of  nutriment  ex- 
ceeding a  narrow  limit;  and  its  possible  increments  of  growth 
being  small  to  set  out  with,  and  rapidly  decreasing,  must 
come  to  an  end  before  any  considerable  size  is  attained. 
Manifestly  the  young  lion,  born  of  tolerable  bulk,  suckled  un- 
til much  bigger,  and  fed  until  half- grown,  is  enabled  by  the 
power  and  organization  which  he  thus  gets  gratis,  to  catch 
and  kill  animals  of  size  enough  to  give  him  the  large  supply 
of  nutriment  needed  to  meet  his  large  expenditure,  and  yet 
leave  a  large  surplus  for  growth.      Thus  then  is  explained 


GROWTH.  131 

the  above-named  contrast  between  the  ox  and  the  sheep.  A 
calf  and  a  lamb  commence  their  physiological  transactions  on 
widely  different  scales ;  their  first  increments  of  growth  are 
similarly  contrasted  in  their  amounts  ;  and  the  two  diminish- 
ing series  of  such  increments,  end  at  similarly-contrasted 
limits. 

§  49.  Such  are  the  several  conditions  by  which  the  phe- 
nomena of  growth  are  governed.  Conspiring  and  conflicting 
in  endless  different  ways  and  degrees,  they  in  every  case 
qualify  more  or  less  differently  each  other's  effects.  Hence 
it  happens  that  we  are  obliged  to  state  each  generalization  as 
true  on  the  average,  or  to  make  the  proviso — other  things 
equal. 

Understood,  in  this  qualified  form,  our  conclusions  are 
these.  First,  that  growth  being  an  integration  with  the 
organism,  of  such  environing  matters  as  are  of  like  nature 
with  the  matters  composing  the  organism,  its  growth  is  de- 
pendent on  the  available  supply  of  such  matters  :  this  is  alike 
a  truth  established  by  experience,  and  an  inference  from  the 
truth  given  in  our  forms  of  thought  (First  Principles,  §  67). 
Second,  that  the  available  supply  of  assimilable  matter  being 
the  same,  and  other  conditions  not  dissimilar,  the  degree  of 
growth  varies  according  to  the  surplus  of  nutrition  over  ex- 
penditure— a  generalization  which  is  illustrated  in  some  of 
the  broader  contrasts  between  different  divisions  of  organ- 
isms, and  is  a  direct  corollary  from  the  persistence  of  force. 
Third,  that  in  the  same  organism,  the  surplus  of  nutrition 
over  expenditure  is  a  variable  quantity ;  and  that  growth  is 
unlimited  or  has  a  definite  limit,  according  as  the  surplus 
docs  or  does  not  progressively  decrease.  This  proposition  we 
found  on  the  one  hand  exemplified  by  the  unceasing  growth 
of  organisms  that  do  not  expend  force ;  by  the  growth,  slowlv 
diminishing  but  never  completely  ceasing,  of  organisms  that 
expend  comparatively  little  force ;  and  by  the  definitely 
limited  growth  of  organisms  that  expend  much  force ;  and 


132  THE    INDUCTIONS    OF    BIOLOGY. 

on  the  other  hand,  we  found  it  to  follow  from  a  certain  rela 
tive  increase  of  expenditure  that  necessarily  accompanies  in 
crease  of  bulk,  and  to  be  therefore  an  indirect  corollary  from 
the  persistence  of  force.  Fourth,  that  among  organisms 
which  are  large  expenders  of  force,  the  size  ultimately  at- 
tained is,  other  things  equal,  determined  by  the  initial  size  : 
in  proof  of  which  conclusion  we  have  abundant  facts,  as  well, 
as  the  a  priori  necessity  that  the  sum-totals  of  analogous 
diminishing  series,  must  depend  upon  the  amounts  of  their 
initial  terms.  Fifth,  that  where  the  likeness  of  other  cir- 
cumstances permits  a  comparison,  the  possible  extent  of 
growth  depends  on  the  degree  of  organization  :  an  inference 
testified  to  by  the  larger  forms  among  the  various  divisions 
and  sub-divisions  of  organisms;  and  inferable  a  priori  from 
the  conditions  of  existence. 


CHAPTER  II. 


DEVELOPMENT* 


§  50.     Certain  general  aspects  of  Development  may  "be 

studied  apart  from  any  examination  of  internal  structures. 

These  fundamental  contrasts  between  the  modes  of  arrange- 
rs 

ment  of  parts,  originating,  as  they  do,  the  leading  external 
distinctions  among  the  various  forms  of  organization,  will  be 
best  dealt  with  at  the  outset.  If  all  organisms  have  arisen 
by  Evolution,  it  is  of  course  not  to  be  expected  that  such 
several  modes  of  development  can  be  absolutely  demarcated : 
we  may  be  sure  of  finding  them  united  by  transitional  modes. 
But  premising  that  a  classification  of  modes  can  but  approx- 
imately represent  the  facts,  we  shall  find  our  general  con- 
ceptions of  Development  aided  by  one. 

Development  is  primarily  central.  All  organic  forms  of 
which  the  entire  history  is  known,  set  out  with  a  symmetri- 
cal arrangement  of  parts  round  a  centre.  In  organisms  of 
the  lowest  grade,  no  other  mode  of  arrangement  is  ever 
definitely  established;  and  in  the  highest  organisms,  central 
development,  though  subordinate  to  another  mode  of  de- 
velopment, continues  to  be  habitually  shown  in  the  changes  of 

*  In  ordinary  speech,  Development  is  often  used  as  synonymous  with  Growth. 
It  hence  seems  needful  to  say,  that  Development  as  here  and  hereafter  used, 
means  increase  of  structure,  and  not  increase  of  bulk.  It  may  be  added,  that  the 
word  Evolution,  comprehending  Growth  as  well  as  Development,  is  to  be  reserved 
foi  occasions  when  both  are  implied 


134  THE    INDUCTIONS   OF    BIOLOGY. 

minute  structure.  Let  us  glance  at  these  propositions  in  the 
concrete.  Leaving  out  those  Rhizopods  which  are 

wholly  structureless,  every  plant  and  animal  in  its  earliest 
stage,  consists  of  a  spherical  sac,  full  of  liquid  containing 
organic  matter,  in  which  is  suspended  a  nucleated  cell,  more 
or  less  distinct  from  the  rest ;  and  the  first  changes  that 
occur  in  the  germ  thus  constituted,  are  changes  that  take 
place  round  centres  produced  by  division  of  the  original 
centre.  From  this  type  of  structure,  the  simplest  organisms 
do  not  depart ;  or  depart  in  no  definite  or  conspicuous  ways. 
Among  plants,  the  Uredo  and  the  several  tribes  of  Protococci 
permanently  maintain  such  a  central  distribution ;  while 
among  animals,  it  is  permanently  maintained  by  crea- 
tures like  the  Gregarina,  and  in  a  different  manner  by  the 
Amceba,  Actiaophrys,  and  their  allies.  In  larger  organisms, 
made  up  chiefly  of  units  that  are  analogous  in  structure  to 
these  simplest  organisms,  the  formation  of  units  ever  continues 
to  take  place  round  points  or'  nuclei ;  though  the  arrangement 
of  these  units  into  groups  and  wholes  may  proceed  after 
another  method. 

Central  development  may  be  distinguished  into  unicentral 
and  multicentral ;  according  as  the  product  of  the  original 
germ,  develops  symmetrically  round  one  centre,  or  develops 
without  subordination  to  one  centre — develops,  that  is,  in 
subordination   to   many   centres.  Unicentral   de- 

velopment, as  displayed  not  in  the  formation  of  single  cells 
but  in  the  formation  of  aggregates,  is  not  common.  The 
animal  kingdom  shows  it  only  in  the  small  group  named 
Thalassicollce :  inert,  spherical  masses  of  jelly,  with  scarcely 
any  organization,  which  are  found  floating  in  southern  seas. 
It  is  feebly  represented  in  the  vegetal  kingdom  by  the  Vol- 
vox  ylobator.  On  the  other  hand,  multicentral  devel- 

opment, or  development  round  insubordinate  centres,  is  va- 
riously exemplified  in  both  divisions  of  the  organic  world.  It 
is  exemplified  in  two  distinct  ways,  according  as  the  insubor- 
dination among  the  centres  of  development  is  partial  or  totaJ 


DEVELOPMENT.  135 

"We  may  most  conveniently  consider  it  under  the  heads  hence 
arising. 

Total  insubordination  among  the  centres  of  develccinert, 
is  shown  where  the  units  or  cells,  as  fast  as  the}r  are  severally 
formed,  part  company  and  lead  independent  lives.  This,  in 
the  vegetal  kingdom,  habitually  occurs  among  the  Proto- 
phyta;  and  in  the  animal  kingdom,  among  the  Proto- 
zoa. Partial  insubordination  is  seen  in  those 
somewhat  advanced  organisms,  that  consist  of  units  which, 
though  they  have  not  separated,  have  so  little  mutual  depend- 
ence that  the  aggregate  they  form  is  irregular.  Among 
plants,  the  Thallogens  very  generally  exemplify  this  mode  of 
development.  Lichens,  spreading  with  flat  or  corrugated 
edges  in  this  or  that  direction,  as  the  conditions  determine, 
have  no  manifest  co-ordination  of  parts.  In  the  Algce,  the 
Nostocs  similarly  show  us  an  unsymmetrical  structure.  Of 
Fungi,  the  sessile  and  creeping  kinds  display  no  further 
dependence  of  one  part  on  another,  than  is  implied  by  their 
cohesion.  And  even  in  such  better-organized  plants  as  the 
Marchantia,  the  general  arrangement  shows  no  reference  to  a 
directive  centre.  Among  animals,  many  of  the  Sponges  may 
be  cited  as  being  thus  devoid  of  that  co-ordination  implied 
by  symmetry:  the  Amoeba-like  units  composing  them,  though 
they  have  some  subordination  to  local  centres,  have  no  subor- 
dination to  a  general  centre.  To  distinguish  that 
kind  of  development  in  which  the  whole  product  of  a  germ 
coheres  in  one  mass,  from  that  kind  of  development  in  which 
it  does  not,  Professor  Huxley  has  introduced  the  words  "  con- 
tinuous "  and  "  discontinuous ;"  and  these  seem  the  best  fitted 
for  the  purpose.  Multicentral  development,  then,  is  divisible 
into  continuous  and  discontinuous. 

From  central  development  we  pass  insensibly  to  that  higher 
kind  of  development  for  which  axial  seems  the  most  appro- 
priate name.  A  tendency  towards  this  is  vaguely  manifested 
almost  eveiy where.  The  great  majority  even  of  Protop/ryta 
anil  P>  otozoa  have  different  longitudinal  and  transverse  di- 


136  THE    INDUCTIONS   OF    BIOLOGY. 

mensions — have  an  obscure  if  not  a  distinct  axial  otructum 
The  originally  cellular  units  out  of  which  higher  organisme 
are  mainly  built  up,  usually  pass  into  shapes  that  are  subordi- 
nated to  lines  rather  than  to  points.  And  in  the  higher  organ- 
isms, considered  as  wholes,  an  arrangement  of  parts  in  rela- 
tion to  an  axis  is  distinct  and  nearly  universal.  We  see  it  in 
the  superior  orders  of  Thallogens  ;  and  in  all  the  Acrogens, 
Endogens,  and  Exogens.  With  few  exceptions  the  Ccelente- 
rata  clearly  exhibit  it ;  it  is  traceable,  though  less  conspicu- 
ously, throughout  the  Mollusea;  and  the  Annulosa  and 
Vertebrata  uniformly  show  it  with  perfect  definiteness. 

This  kind  of  development,  like  the  first  kind,  is  of  two 
orders.  The  whole  germ-product  may  arrange  itself  round 
a  single  axis,  or  it  may  arrange  itself  round  many  axes ;  the 
structure  may  be  uniaxial  or  multiaxial.  Each  division  of 
the  organic  kingdom  furnishes  examples  of  both  these  or- 
ders. In  such  Fungi  as  exhibit  axial  development  at 
all,  we  commonly  see  development  round  a  single  axis.  Some 
of  the  Alga;,  as  the  common  tangle,  show  us  this  arrange- 
ment. And  of  the  higher  plants,  many  Endogens  and 
small  Exogens  are  uniaxial.  Of  animals,  the  advanced  are 
without  exception  in  this  category.  There  is  no  known  ver- 
tebrate in  which  the  whole  of  the  germ- product  is  not  subor- 
dinated to  a  single  axis.  In  the  more  fully-organized  Annu- 
losa, the  like  is  almost  universal ;  as  it  is  also  in  the  superior 
orders  of  Mollusea.  Multiaxial  development  occurs 
in  most  of  the  plants  we  are  familiar  with — every  branch  of 
a  shrub  or  tree  being  an  independent  axis.  But  while  in  the 
vegetal  kingdom,  multiaxial  development  prevails  among  the 
highest  types;  in  the  animal  kingdom,  it  prevails  only  among 
the  lowest  types.  It  is  extremely  general,  if  not  universal, 
among  the  Ccelenterata ;  it  is  characteristic  of  the  Mollus- 
coida ;  among  Molluscs  the  compound  Ascidians  exhibit  it ; 
and  it  is  seen,  though  under  another  form,  in  the  inferior 
Annulosa. 

Development  that  is  axial,  like  development  that  is  centraL 


DEVELOPMENT.  137 

may  be  either  continuous  or  discontinuous  :  the  parts  having 
different  axes  may  continue  united,  or  they  may  separate. 
Instances  of  each  alternative  are  supplied  by  both  plants 
and  animals.  Continuous,  multiaxial  development,  is 

that  which  plants  usually  display  ;  and  need  not  be  illustrated 
Further  than  by  reference  to  every  garden.  As  cases  of  it  in 
animals  may  be  named,  all  the  compound  Hijdrozoa  and  Ac- 
tinozoa;  and  such  molluscous  forms  as  the  BotrylUdie.  Of 

multiaxial  development  that  is  discontinuous,  a  familiar 
instance  among  plants  exists  in  the  common  strawberry. 
This  sends  out  over  the  neighbouring  surface,  long  slender 
shoots,  bearing  at  their  extremities  buds  that  presently  strike 
roots,  and  become  new  individuals ;  and  these  by  and  by  lose 
their  connexions  with  the  original  axis.  Other  plants  there 
are  that  produce  certain  specialized  buds  called  bulbils,  which 
separating  themselves  and  falling  to  the  ground,  grow  into 
independent  plants.  Among  animals  the  fresh- water  polype 
very  clearly  shows  this  mode  of  development :  the  young 
polypes,  budding  out  from  its  surface,  severally  arrange 
their  parts  around  distinct  axes,  and  eventually  detaching 
themselves,  lead  separate  lives,  and  produce  other  polypes 
after  the  same  fashion.  By  some  of  the  lower  Annulosa,  this 
multiplication  of  axes  from  an  original  axis,  is  carried  on  after 
a  different  manner  :  the  string  of  segments  spontaneously 
divides ;  and  after  further  growth,  division  recurs  in  one  or 
both  of  the  halves.  And  in  the  Aphides,  we  have  a  still  fur- 
ther modification  of  this  process. 

Grouping  together  its  several  modes  as  above  delineated, 
we  see  that 

Central 
Development  is  \       or 
Axial 


10 


Unicentral 

or 

r     Continuous 

Multicentral  ■ 

or 

I 

L  Discontinuous 

Uniaxial 

or             i 

r     Continuous 

Multiaxial     ' 

or 

I 

^  Discontinuous 

lo3  THE    INDUCTIONS    OF    BIOLOGY. 

Any  one  adequately  acquainted  with  the  facts,  may  readily 
raise  objections  to  this  arrangement.  He  may  name  forma 
which  do  not  obviously  come  under  any  of  these  heads.  He  may 
point  to  plants  that  are  for  a  time  multicentral,  but  after- 
wards develop  axially.  And  from  lower  types  of  animals,  he 
may  choose  many  in  which  the  continuous  and  discontinuous 
modes  are  both  displayed.  But,  as  already  hinted,  an  ar- 
rangement free  from  such  anomalies  must  be  impossible,  if  the 
various  orders  of  organization  have  arisen  by  Evolution.  The 
one  above  sketched  out,  is  to  be  regarded  as  only  a  rough 
grouping  of  the  facts,  which  helps  us  to  a  conception  of  them 
in  their  totality ;  and  so  regarded,  it  will  be  of  service  when 
we  come  to  treat  of  Individuality  and  Reproduction. 

§  51.  From  these  most  general  external  aspects  of  organic 
development,  let  us  now  turn  to  its  internal  and  more  special 
aspects.  When  treating  of  Evolution  as  a  universal  process 
of  things,  a  rude  outline  of  the  course  of  structural  changes  in 
organisms  was  given  (First  Principles,  §§  43,  55,  56).  Here, 
however,  it  will  be  proper  to  describe  these  changes  more  fully. 

The  bud  of  any  common  plant  in  its  earliest  stage,  consists 
of  a  small  hemispherical  or  sub-conical  projection.  While 
it  increases  most  rapidly  at  the  apex,  this  presently  deve- 
lops on  one  side  of  its  base,  a  smaller  projection  of  like  general 
shape  with  itself.  Here  is  the  rudiment  of  a  leaf ;  which  pre- 
sently spreads  more  or  less  round  the  base  of  the  central 
hemisphere  or  main  axis.  At  the  same  time  that  the  central 
hemisphere  rises  higher,  this  lateral  prominence,  also  in- 
creasing, gives  rise  to  subordinate  prominences  or  lobes. 
These  are  the  rudiments  of  stipules,  where  the  leaves  are 
stipulated.  Meanwhile,  towards  the  other  side  of  the  main 
axis,  and  somewhat  higher  up,  another  lateral  prominence 
arising,  marks  the  origin  of  a  second  leaf.  By  the  time  that 
the  first  leaf  has  produced  another  pair  of  lobes,  and  the 
second  leaf  has  produced  its  primary  pair,  the  central  hemi- 
sphere, still  increasing  at  its  apex,  exhibits  the  rudiment  of  a 


DEVELOPMENT.  1-39 

third  leaf.  Similarly  throughout.  While  the  g(  rm  of  each 
succeeding  leaf  thus  arises,  the  germs  of  the  previous  leaves, 
in  the  order  of  their  priority,  are  changing  their  rude  nodu- 
lated shapes  into  flattened-out  expansions  ;  which  slowly  put 
on  those  sharp  outlines  they  show  when  unfolded.  Thna 
from  that  extremely  indefinite  figure,  a  rounded  lump,  giving 
off  from  time  to  time  lateral  lumps,  which  severally  becoming 
symmetrically  lobed,  gradually  assume  specific  and  involved 
forms,  we  pass  little  by  little  to  that  comparatively  complex 
tiling — a  leaf- bearing  shoot.  Internally,  a  bud  under- 

goes analogous  changes.  The  layer  of  substance  which  forms 
the  surface  of  the  hemisphere,  and  in  which  these  metamor- 
phoses commence,  consists  of  a  transparent,  irregularly-aggre- 
gated mass  of  cells  and  centres  of  growth,  not  formed  into  a 
tissue.  Especially  is  this  the  case  at  the  apex,  where  the 
vital  activity  is  the  greatest.  Here  the  primitive  cellular 
mass  passes  without  any  line  of  demarcation  into  the  tissues 
that  are  developing  from  it.  While,  by  continued  cell-multi- 
plication this  la}rer  increases,  and  doing  so  most  rapidly  al 
the  apex  thrusts  outwards  its  lateral  portions,  these  begin  to 
exhibit  differentiations.  "  Gradually,"  says  Schleiden,  "  se- 
parate masses  of  cells,  with  a  distinct  and  definite  outline, 
appear  in  this  chaos,  and  they  cease  to  partake  of  the  process 
of  growth  going  on.  At  first  the  epidermis  is  separated, 
then  the  vascular  bundles,  later  the  parenchyma."  Similarly 
with  the  lateral  buds  whence  leaves  arise.  In  the,  at  first,  un- 
organized mass  of  cells  constituting  the  rudimentary  leaf, 
there  are  formed  vascular  bundles  which  eventually  become 
the  veins  of  the  leaf;  and  gradually  there  appear  also,  though 
La  ways  that  have  not  been  specified,  the  parenchyma  and  the 
epithelium.  Nor  do  we  fail  to  find   an  essentially 

parallel  tet  of  changes,  when  we  trace  the  histories  of  the  in- 
dividual cells.  While  the  tissues  they  compose  are  separ- 
ating, the  cells  are  growing  step  by  step  more  unlike. 
Some  become  flat,  some  polyhedral,  some  cylindrical,  some 
prismatic,  some  spindle-shnped.     These  develop  spiral   fibres 


140  THE    INDUCTIONS    OF    BIOLOGY. 

in  their  interiors  ;  and  those,  net-works  of  fibres.  Here  a 
number  of  cells  unite  together  to  form  a  tube;  and  there 
they  become  solid  by  the  internal  deposition  of  woody  or  other 
matter.  Through  such  changes,  too  numerous  and  involved 
to  be  here  detailed,  the  originally  uniform  cells  go  on  diverg- 
ing and  re-diverging,  until  there  are  produced  various  forms 
that  seem  to  have  very  little  in  common. 

The  arm  of  a  man  makes  its  first  appearance  in  as  simple 
a  way  as  does  the  shoot  of  a  plant.     According  to  Bischoff,  it 
buds-out  from  the  side  of  the  embryo,  as  a  little  tongue-shaped 
projection,  presenting  no  differences  of  parts  ;  and  it  might 
serve  for  the  rudiment  of  some  one  of  the  various  other  organs 
that  also  arise  as  buds.     Continuing  to  lengthen,  it  presently 
becomes  somewhat  enlarged  at  its  end ;  and  is  then  described  as 
a  pedicle  bearing  a  flattened,  round-edged  lump.  This  lump  is 
the  representative  of  the  future  hand  ;  and  the  pedicle,  of  the 
future  arm.     By  and  by,  at  the  edges  of  this  flattened  lump, 
there  appear  four  clefts,  dividing  from  each  other  the  buds  of 
the  future  fingers  ;  and  the  hand  as  a  whole  grows  a  littl  3 
more  distinguishable  from  the  arm.     Up  to  this  time,  th3 
pedicle  has  remained  one  continuous  piece  ;  but  it  now  begins 
to  show  a  bend  at  its  centre,  which  indicates  the  division  into 
arm  and  forearm.     The  distinctions  thus  rudely  indicated, 
gradually  increase  :  the  fingers  elongate  and  become  jointed  ; 
and   the  proportions  of  all  the  parts,  originally  very  un- 
like  those   of  the   complete   limb,  slowly    approximate    to 
them.  During  its  bud-like  stage,  the  rudimentary 

arm  is  nothing  but  a  Homogeneous  mass  of  simple  cells,  with- 
out any  arrangement.  By  the  diverse  changes  they  gradually 
undergo,  these  cells  are  transformed  into  bones,  muscles, 
blood-vessels,  and  nerves.  The  extreme  softness  and  delicacy 
of  this  primary  cellular  tissue,  renders  it  difficult  to  trace  the 
initial  stages  of  these  differentiations.  In  consequence  of  the 
colour  of  their  contents,  the  blood-vessels  are  the  first  parw  to 
become  visible.  Afterwards  the  cartilaginous  parts,  wHeh 
are  the  bases  of  the  future  bones,  become  marked  out  by  the 


DEVELOPMENT.  HI 

denser  aggregation  of  their  constituent  cells,  and  the  produc- 
tion between  these  of  a  hyaline  substance  which  unites  them 
into  a  translucent  mass.  When  first  perceptible,  the  muscles 
are  gelatinous,  pale,  yellowish,  transparent,  and  indistinguish- 
able from  their  tendons.  The  various  other  tissues  of  which 
the  arm  cons'sts,  beginning  with  very  faintly-marked  differ- 
ences, become  day  by  day  more  definite  in  their  outlines  and 
appearances.  In   like  manner,  the  units  composing 

f.hese  tissues,  severally  assume  increasingly-specific  characters. 
The  fibres  of  muscle,  at  first  made  visible  in  the  midst  of 
their  gelatinous  matrix  only  by  immersion  in  alcohol,  grow 
more  numerous  and  distinct ;  and  by  and  by  they  begin  to 
exhibit  transverse  stripes.  The  bone-cells  put  on  by  degrees 
tneir  curioua  structure  of  branching  canals.  And  so  in  their 
respective  ways  with  the  units  of  skin  ana  the  rest. 

Thus  in  each  of  the  organic  sub-kingdoms,  we  see  this 
change  from  an  incoherent,  indefinite  homogeneity,  to  a 
coherent,  definite  heterogeneity,  illustrated  in  a  quadruple 
way.  The  originally -like  units  or  cells,  become  unlike  in 
various  ways,  and  in  ways  more  numerous  and  marked  as  the 
development  goes  on.  The  several  tissues  which  these 
several  classes  of  cells  form  by  aggregation,  grow  little  by 
little  distinct  from  each  other ;  and  little  by  little  put  on 
those  structural  complexities,  that  arise  from  differentiations 
among  their  component  units.  In  the  shoot,  as  in  the  limb, 
the  external  form,  originally  very  simple,  and  having  much 
in  common  with  countless  simple  forms,  organic  and  in- 
organic, gradually  acquires  an  increasing  complexity,  and  an 
increasing  unlikeness  to  other  forms.  And  meanwhile,  the 
remaining  parts  of  the  organism  to  which  the  shoot  or  limb 
belongs,  having  been  severally  assuming  structures  divergent 
from  each  other  and  from  that  of  this  particular  shoot  or 
limb,  there  has  arisen  a  greater  heterogeneity  in  the  organ- 
Ism  as  a  whole. 

$  52.     One  of  the  most  remarkable  inductions  of  embry- 


142  THE    INDUCTIONS    OF    BIOLOGY. 

ology.  comes  next  in  order.  Yon  Baer  found  that  in  its 
earliest  stage,  every  organism  has  the  greatest  number  of 
characters  in  common  with  all  other  organisms  in  their 
earliest  stages  ;  that  at  a  stage  somewhat  later,  its  structure 
is  like  the  structures  displayed  at  corresponding  phases  by  a 
less  extensive  multitude  of  organisms  ;  that  at  each  sub- 
sequent stage,  traits  are  acquired  which  successively  distin- 
guish the  developing  embryo  from  groups  of  embryos  that  it 
previously  resembled — thus  step  by  step  diminishing  the 
group  of  embryos  which  it  still  resembles  ;  and  that  thus  the 
class  of  similar  forms,  is  finally  narrowed  to  the  species  of 
which  it  is  a  member.  This  abstract  proposition  will  per- 
haps not  be  fully  realized  by  the  general  reader.  It  will  be 
best  to  re-state  it  in  a  concrete  shape.  The  germ 

out  of  which  a  human  being  is  evolved,  differs  in  no  visible 
respect  from  the  germ  out  of  which  every  animal  and  plant  is 
evolved.  The  first  conspicuous  structural  change  undergone 
by  this  human  germ,  is  one  characterizing  the  germs  of 
animals  only — differentiates  them  from  the  germs  of  plants. 
The  next  distinction  established,  is  a  distinction  exhibited  by 
all  Vertebrata;  but  never  exhibited  by  Annulosa,  Mollutca,  or 
Ccelenterata.  Instead  of  continuing  to  resemble,  as  it  now 
does,  the  rudiments  of  all  fishes,  reptiles,  birds,  and  mammals ; 
this  rudiment  of  a  man,  assumes  a  structure  that  is  seen  onlv 
in  the  rudiments  of  mammals.  Later,  the  embryo  undergoes 
changes  which  exclude  it  from  the  group  of  implacental 
mammals  ;  and  prove  that  it  belongs  to  the  group  of  placental 
mammals.  Later  still,  it  grows  unlike  tlie  embryos  of  those 
placental  mammals  distinguished  as  ungulate  or  hoofed  ;  and 
continues  to  resemble  only  the  unguiculate  or  clawed.  .By 
and  by,  it  ceases  to  be  like  any  foetuses  but  those  of  the  cpad- 
rumana ;  and  eventually  the  foetuses  of  only  the  3  lgher 
quadrumana  are  simulated.  Lastly,  at  birth,  the  ('nfaut, 
belonging  to  whichever  human  race  it  may  do,  is  struci  urally 
very  much  like  the  infants  of  all  other  human  race;  ;  and 
only  afterwards  acquires  those  various  minor  peculiarities  of 


DEVELOPMENT.  14^ 

form  that  distinguish  the  variety  of  man  to  which  it  be- 
longs. 

The  generalization  here  expressed  and  illustrated,  must 
not  be  confounded  with  an  erroneous  semblance  of  it  that  has 
obtained  considerable  currency.  An  impression  has  been~~ 
given  by  those  who  have  popularized  the  statements  of  em- 
In  yologists,  that  during  its  development,  each  higher  organ- 
ism passes  through  stages  in  which  it  resembles  the  adult 
forms  of  lower  organisms — that  the  embryo  of  a  man  is  at 
one  time  like  a  fish,  and  at  another  time  like  a  reptile.  This 
is  not  the  fact.  The  fact  established  is,  that  up  to  a  certain 
point,  the  embryos  of  a  man  and  a  fish  continue  similar,  and 
that  then  differences  begin  to  appear  and  increase — the  one 
embryo  approaching  more  and  more  towards  the  form  of  a 
fish  ;  the  other  diverging  from  it  more  and  more.  And  so 
with  the  resemblances  to  the  more  advanced  types.  Suppos- 
ing the  germs  of  all  kinds  of  organisms  to  be  simultaneously 
developing,  we  may  say  that  all  members  of  the  vast  mul- 
titude take  their  first  steps  in  the  same  direction  ;  that'  at  the 
second  step  one-half  of  this  vast  multitude  diverges  from  the 
other  half,  and  thereafter  follows  a  different  course  of  deve- 
lopment ;  that  the  immense  assemblage  contained  in  either 
of  these  divisions,  very  soon  again  shows  a  tendency  to  take 
two  or  more  routes  of  development ;  that  each  of  the  two  or 
more  minor  assemblages  thus  resulting,  shows  for  a  time  but 
small  divergences  among  its  members,  but  presently  again 
divides  into  groups  which  separate  ever  more  widely  as  they 
progress ;  and  so  on,  until  each  organism,  when  nearly  com- 
plete, is  accompanied  in  its  further  modifications  only  by 
organisms  of  the  same  species  ;  and  last  of  all,  assumes  the 
peculiarities  which  distinguish  it  as  an  individual — diverges 
to  a  slight  extent  to  the  organisms  it  is  most  like.  The 

reader  must  also  be  cautioned  against  accepting  this  general- 
ization as  exact.  The  likenesses  thus  successively  displayed 
are  not  precise  but  approximate.  Only  leading  characteris- 
tics are  the  same  :  not  all  the  details.      It  is  as  though  in 


144  THE    INDUCTIONS   OF    BIOLOGY. 

one  of  the  diverging  groups  just  described,  each  kind  of 
organism,  though  having  a  general  direction  of  development 
like  that  of  the  others  it  is  for  a  time  travelling  with,  shows 
from  the  first  a  tendency  to  leave  the  general  route — a  tend- 
ency which  presently  becomes  strongly  marked.  Making 
all  requisite  qualifications,  however,  these  resemblances  re- 
main conspicuous ;  and  the  fact  that  they  follow  each  other 
in  the  way  described,  is  a  fact  of  great  significance. 

§  53.  This  comparison  between  the  course  of  development 
in  any  creature,  and  the  course  of  development  in  all  other 
creatures — this  arrival  at  the  conclusion  that  the  course  of 
development  in  each,  at  first  the  same  as  in  all  others,  be- 
comes stage  by  stage  differentiated  from  the  courses  of  all 
others,  brings  us  within  view  of  an  allied  conclusion.  If  we 
contemplate  the  successive  stages  passed  through  by  any 
higher  organism,  and  observe  the  relation  between  it  and  its 
environment  at  each  of  these  stages ;  we  shall  see  that  this  re- 
lation is  modified  in  a  way  analogous  to  that  in  which  the 
relation  between  the  organism  and  its  environment  is  modi- 
fied, as  we  advance  from  the  lowest  to  the  highest  grades. 
Along  with  the  progressing  differentiation  of  each  organism 
from  others,  we  find  a  progressing  differentiation  of  it 
from  its  environment ;  like  that  progressing  differentiation 
from  the  environment  which  we  meet  with  in  the  ascending 
forms  of  life.  Let  us  first  glance  at  the  way  in  which  the 
ascending  forms  of  life  exhibit  this  progressing  differentiation 
from  the  environment. 

In  the  first  place,  it  is  illustrated  in  structure.  Ad- 
vance from  the  homogeneous  to  the  heterogeneous,  itself  in- 
volves an  increasing  distinction  from  the  inorganic  world. 
In  the  lowest  Protozoa  we  have  a  simplicity  approaching 
to  that  of  air,  water,  or  earth  ;  and  the  ascent  to  organisms 
of  greater  and  greater  complexity  of  structure,  is  an  ascent  to 
organisms  that  are  in  that  respect  more  strongly  contrasted 
with  the  structureless  environment.  Inform,  again, 


DEVELOPMENT.  143 

we  see  the  same  fact.  An  ordinary  characteristic  of  inor- 
ganic matter  is  its  indefiniteness  of  form ;  and  this  is  also  a 
characteristic  of  the  lower  organisms,  as  compared  with  the 
higher.  Speaking  generally,  plants  are  less  definite  than 
animals,  both  in  shape  and  size — admit  of  greater  modifica- 
tions from  variations  of  position  and  nutrition.  Among  ani- 
mals, the  simplest  Rhizopods  are  not  only  structureless  bat 
amorphous  :  the  form  is  never  specific,  and  is  constantly 
changing.  Of  the  organisms  resulting  from  the  aggregation 
of  such  creatures,  we  see  that  while  some,  as  the  Forammi- 
fera,  assume  a  certain  definiteness  of  form,  in  their  shells  at 
least ;  others,  as  the  Sponges,  are  very  irregular.  The  Zoo- 
phytes and  the  Polyzoa  are  compound  organisms,  most  of 
which  have  a  mode  of  growth  not  more  determinate  than  that 
of  plants.  But  among  the  higher  animals,  we  find  not 
only  that  the  mature  shape  of  each  species  is  very  definite, 
but  that  the  individuals  of  each  species  differ  very  little  in 
size.  A  parallel  increase  of  contrast  is  seen  in  chemi- 

cal composition.  With  but  few  exceptions,  and  those  only 
partial  ones,  the  lowest  animal  and  vegetal  forms  are  inhabit- 
ants of  the  water ;  and  water  is  almost  their  sole  constituent. 
Desiccated  Protophyta  and  Protozoa  shrink  into  mere  dust ; 
and  among  the  Acalephes,  we  find  but  a  few  grains  of  solid 
matter  to  a  pound  of  water.  The  higher  aquatic  plants,  in 
common  with  the  higher  aquatic  animals,  possessing  as  they 
do  increased  tenacity  of  substance,  also  contain  a  greater  pro- 
portion of  the  organic  elements  ;  and  so  are  chemically  more 
unlike  their  medium.  And  when  we  pass  to  the  superior 
classes  of  organisms — land-plants  and  land-animals — we  find 
that,  chemically  considered,  they  have  little  in  common  either 
with  the  earth  on  which  they  stand  or  the  air  which  sur- 
rounds them.  In  specific  gravity  too,  we  may  note 
the  like  truth.  The  very  simplest  forms,  in  common  with 
the  spores  and  gemmules  of  higher  ones,  arc  as  nearly  as  may 
he  of  the  same  specific  gravity  as  the  water  in  which  they 
Boat ;    and  though   it  cannot  be  said    that  anion jj  aquatic 


146'  THE    INDUCTIONS   OF    BIOLOGY. 

creatures,  superior  specific  gravity  is  a  standard  of  general 
superiority,  yet  we  may  fairly  say  that  vhe  superior  orders  oi 
them,  when  divested  of  the  appliances  by  which  their  specific 
gravity  is  regulated,  differ  more  from  water  in  their  relative 
weight  than  do  the  lowest.  In  terrestrial  organisms,  tli8 
contrast  becomes  extremely  marked.  Trees  and  plants,  in 
common  with  insects,  reptiles,  mammals,  birds,  are  all  of  a 
specific  gravity  considerably  less  than  that  of  the  earth  and 
immensely  greater  than  that  of  the  air.  Yet  further, 

we  see  the  law  similarly  fulfilled  in  respect  of  temperature. 
Plants  generate  but  extremely  small  quantities  of  heat,  which 
are  to  be  detected  only  by  very  delicate  experiments ;  and 
practically  they  may  be  considered  as  having  the  same  tem- 
perature as  their  environment.  The  temperature  of  aquatic 
animals  is  very  little  above  that  of  the  surrounding  water : 
that  of  the  invertebrata  being  mostly  less  than  a  degree  above 
it,  and  that  of  fishes  not  exceeding  it  by  more  than  two  or 
three  degrees ;  save  in  the  case  of  some  large  red-blooded 
fishes,  as  the  tunny,  which  exceed  it  in  temperature  by  nearly 
ten  degrees.  Among  insects,  the  range  is  from  two  to  ten 
degrees  above  that  of  the  air  :  the  excess  varying  according 
to  their  activity.  The  heat  of  reptiles  is  from  four  to  fifteen 
degrees  more  than  the  heat  of  their  medium.  While  mam  • 
mals  and  birds  maintain  a  heat  which  continues  almost  un- 
affected by  external  variations,  and  is  often  greater  than  that 
of  the  air  by  seventy,  eighty,  ninety,  and  even  a  hundred 
degrees.  Once  more,  in  greater  self-mobility  a  pro- 

gressive differentiation  is  traceable.  The  especial  character* 
istic  by  which  we  distinguish  dead  matter  is  its  inertness : 
some  form  of  independent  motion  is  our  most  general  test  of 
life.  Passing  over  the  indefinite  border-land  between  the 
animal  and  vegetal  kingdoms,  we  may  roughly  class  plants 
as  organisms  which,  while  they  exhibit  that  species  of  motion 
implied  in  growth,  are  not  only  devoid  of  locomotive  power, 
but  with  some  unimportant  exceptions  are  devoid  of  the 
power  of  moving  their  parts  in  relation  to  each  other ;  and 


DEVELOPMENT.  147 

thus  arc  less  differentiated  from  the  inorganic  world  than 
animals.  Though  in  those  microscopic  Protophyta  and  Pro- 
tozoa inhabiting  the  water — the  spores  of  algoe,  the  gemmules 
of  sponges,  and  the  infusoria  generally — we  see  locomotion 
produced  by  ciliary  action  ;  yet  this  locomotion,  while  rapid 
relatively  to  the  size  of  the  creatures,  is  absolutely  slow.  Of 
the  Ccelentcrata,  a  great  part  are  either  permanently  rooted  or 
habitually  stationary  ;  and  so  have  scarcely  any  self-mobility 
but  that  implied  in  the  relative  movements  of  parts ;  while 
the  rest,  of  which  the  common  jelly-fish  will  serve  as  a  sam- 
ple, have  mostly  but  little  ability  to  move  themselves  through 
the  water.  Among  tne  nigher  aquatic  Invertebrate!, — cuttle- 
fishes and  lobsters,  for  instance, — there  is  a  very  considerable 
power  of  locomotion ;  and  the  aquatic  Vertebrata  are,  con- 
sidered as  a  class,  much  more  active  in  their  movements  than 
the  other  inhabitants  of  the  water.  But  it  is  only  when  we 
come  to  air-breathing  creatures,  that  we  find  the  vital  charac 
teristic  of  self-mobility  manifested  in  the  highest  degree. 
Flying  insects,  mammals,  birds,  travel  with  a  velocity  far 
exceeding  that  attained  by  any  of  the  lower  classes  of  ani- 
mals ;  and  so  are  more  strongly  contrasted  with  their  inert 
environment.  Thus,   on  contemplating  the  various 

grades  of  organisms  in  their  ascending  order,  we  find  them 
more  and  more  distinguished  from  their  inanimate  media,  in 
structure,  in  form,  in  chemical  composition,  in  specific  gravity, 
in  temperature,  in  self-mobility.  It  is  true  that  this  general- 
ization does  not  hold  with  complete  regularity.  Organisms 
which  are  in  some  respects  the  most  strongly  contrasted  with 
the  environing  inorganic  world,  are  in  other  respects  less  so 
than  inferior  organisms.  As  a  class,  mammals  are  higher 
than  birds  ;  and  yet  they  are  of  lower  temperature,  and  have 
smaller  powers  of  locomotion.  The  stationary  oyster  is  of 
higher  organization  than  the  free-swimming  medusa  ;  and 
the  cold-blooded  and  less  heterogeneous  fish,  is  quicker  in  its 
movements  than  the  warm-blooded  and  more  heterogeneous 
sloth.      But  the  admission   that  the    several   aspects  undrr 


148  THE    INDUCTIONS    OF    BIOLOGY. 

which  this  increasing  contrast  shows  itself,  bear  variable 
ratios  to  each  other,  does  not  conflict  with  the  general  truth, 
that  as  we  ascend  in  the  hierarchy  of  organisms,  we  meet  with 
not  only  an  increasing  differentiation  of  parts,  but  also  an 
increasing:  differentiation  from  the  surrounding  medium  in 
sundry  other  physical  attributes.  It  would  seem  that  this 
peculiarity  has  some  necessary  connexion  with  superior 
vital  manifestations.  One  of  those  lowly  gelatinous  forms, 
so  transparent  and  colourless  as  to  be  with  difficulty  dis- 
tinguished from  the  water  it  floats  in,  is  not  more  like  its 
medium  in  chemical,  mechanical,  optical,  thermal,  and  other 
properties,  than  it  is  in  the  passivity  with  which,  it  sub- 
mits to  all  the  influences  and  actions  brought  to  bear  upon 
it ;  while  the  mammal  does  not  more  widely  differ  from 
inanimate  things  in  these  properties,  than  it  does  in  the  ac- 
tivity with  which  it  meets  surrounding  changes  by  compens- 
ating changes  in  itself.  And  between  these  two  extremes, 
we  shall  observe  a  constant  ratio  between  these  two  kinds  of 
contrast.  Whence  we  may  say,  that  in  proportion  as  an 
organism  is  physically  like  its  environment,  does  it  remain  a 
passive  partaker  of  the  changes  going  on  in  its  environment ; 
while  in  proportion  as  it  is  endowed  with  powers  of  counter- 
acting such  changes,  it  exhibits  greater  uulikeness  to  its  en- 
vironment.* 

If  now,  from  this  same  point  of  view,  we  consider  the  rela- 
tion borne  to  its  environment  by  any  superior  organism  in 
its  successive  stages,  we  find  an  analogous  series  of.  con- 
trasts. Of  course  in  respect  of  degrees  of  structure,  the 
parallelism  is  complete.  The  difference,  at  first  small,  be- 
tween the  comparatively  structureless  germ  and  the  com- 
paratively structureless  inorganic  world,  becomes  necessarily 
greater,  step  by  step,  as  the  differentiations  of  the  germ  be- 
come more  numerous  and  definite.  How  of  form 
the  like  holds,  is  equally  manifest.      The  sphere,  which  is 

•  This  paragraph  originally  formed  part  of  a  review-article  on  "  Transcenden- 
tal Physiology,"  published  in  ]  857 


DEYI.l.OrMKXT.  149 

the  point  of  departure  common  to  all  organisms,  is  the  most 
generalized  of  figures  ;  and  one  that  is,  under  various  circum- 
stances, assumed  by  inorganic  matter.  While  the  incij)ient 
organism  is  spherical,  it  is  not  only  like  many  particular  in- 
organic masses ;  but  it  is  like  the  rest,  in  the  sense  that  it  has 
the  shape  which  would  result,  were  all  their  irregularities 
averaged.  But  as  it  develops,  it  loses  all  likeness  to  inor- 
ganic objects  in  the  environment ;  and  eventually  becomes 
distinct  even  from  ail  organic  elects  in  its  environ- 
ment. In  specific  gravity,  the  alteration,  though  not 
very  marked,  is  still  in  the  same  direction.  Development 
being  habitually  accompanied  by  a  relative  decrease  in  the 
quantity  of  water,  and  an  increase  in  the  quantity  of  consti- 
tuents that  are  heavier  than  water,  there  results  a  small  aug- 
mentation of  relative  weight.  In  power  of  maintain- 
ing a  temperature  above  that  of  surrounding  things,  the 
differentiation  from  the  environment  that  accompanies  deve- 
lopment, is  marked.  All  ova  are  absolutely  dependent  for 
their  heat  on  external  sources.  Like  inorganic  bodies,  they 
gain  or  lose  heat  according  as  neighbouring  bodies  are  colder 
or  hotter.  The  mammalian  young  is,  during  its  uterine  life, 
dependent  on  the  maternal  heat ;  and  at  birth  has  but  a  par-* 
tial  power  of  making  good  the  loss  by  radiation.  But  as  it 
advances  in  development,  it  gains  an  ability  to  maintain  a 
constant  temperature  above  that  of  surrounding  things  :  so 
becoming  markedly  unlike  all  surrounding  things,  save  or- 
ganisms of  allied  nature.  Lastly,  in  self- mobility  this 
increasing  contrast  is  not  less  decided.  Save  in  a  few  aber- 
rant tribes,  chiefly  parasitic,  we  find  the  general  fact  to  be, 
that  the  locomotive  power,  totally  absent  or  very  small  at  the 
outset,  increases  with  the  advance  towards  maturity?  The 
more  highly  developed  the  organism  becomes,  the  stronger 
grows  the  contrast  between  its  activity  and  the  inertness  of 
the  objects  amid  which  it  moves. 

Thus  we  may  say  that  the  development  of  an  individual 
organism,  is  at  the  same  time  a  differentiation  of  its  parts 


lf>0  THE    INDUCTIONS    OF    BIOLOGY. 

from  each,  other,  and  a  differentiation  of  the  consolidated 
whole  from  the  environment ;  and  that  in  the  last  as  in  the 
first  respect,  there  is  a  general  analogy  between  the  progres- 
sion of  an  individual  organism,  and  the  progression  from  the 
lowest  orders  of  organisms  to  the  highest  orders.  It 

may  be  remarked  that  some  kinship  seems  to  exist  between 
these  generalizations  and  the  doctrine  of  Schelling,  that  Life 
is  the  tendency  to  individuation.  For  evidently,  in  becom- 
ing more  distinct  from  each  other,  and  from  their  environ- 
ment, organisms  acquire  more  marked  individualities.  As 
far  as  I  can  gather  from  outlines  of  his  philosophy,  however, 
it  appears  that  Schelling  entertained  this  conception  in  a 
general  and  transcendental  sense,  rather  than  in  a  special  and 
scientific  one. 

§  54.  The  deductive  interpretations  of  these  general  facts 
of  development,  in  so  far  as  they  are  at  present  possible,  must 
be  postponed  until  we  arrive  at  the  fourth  and  fifth  divisions  of 
this  work  ;  which  will  be  chiefly  occupied  with  them.  There 
are,  however,  one  or  two  general  aspects  of  these  inductions, 
^  which  maybe  here  most  conveniently  dealt  with  deductively. 

The  general  law  of  development  as  displayed  in  organisms, 
is  readily  shown  to  be  necessary,  if  the  initial  and  terminal 
stages  are  such  as  we  know  them  to  be.  Grant  that  each 
organism  is  at  the  outset  homogeneous,  and  that  when  com- 
plete it  is  relatively  heterogeneous ;  and  of  necessity  it  fol- 
lows that  development  is  a  change  from  the  homogeneous 
to  the  heterogeneous — a  change  during  which  there  must  be 
gone  through  all  the  infinitesimal  gradations  of  heterogeneity 
that  lie  between  these  extremes.  If,  again,  there  is  at  first 
indefiifiteness,  and  at  last  definiteness,  the  transition  cannot 
but  be  from  the  one  to  the  other  of  these,  through  all  intermedi- 
ate degrees  of  definiteness.  Further,  if  the  parts,  originally 
incoherent  or  uncombined,  eventually  become  relatively  co- 
herent or  combined ;  there  must  be  a  continuous  increase  of 
coherence  or  combination.      Ilence  the  general   truth  thai 


DEVELOPMENT.  151 

development  is  a  change  from  incoherent,  indefinite  homo- 
geneity, to  coherent,  definite  heterogeneity,  becomes  a  self- 
evident  one,  when  observation  has  shown  us  the  state  in 
which  organisms  begin,  and  the  state  in  which  they  end. 

Just  in  the  same  way  that  the  growth  of  an  entire  organ- 
ism, is  carried  on  by  abstracting  from  the  environment 
substances  like  those  composing  the  organism ;  so  the  pro- 
duction of  each  organ  within  the  organism,  is  carried  on  by 
abstracting  from  the  substances  contained  in  the  organism, 
those  required  by  this  particular  organ.  Each  organ  at  the 
expense  of  the  organism  as  a  whole,  integrates  with  itself 
certain  special  kinds  and  proportions  of  the  matters  circulat- 
ing around  it ;  in  the  same  way  that  the  organism  as  a 
whole,  integrates  with  itself  certain  special  kinds  and  propor- 
tions of  matters  at  the  expense  of  the  environment  as  a 
whole.  So  that  the  organs  are  qualitatively  differentiated 
from  each  other,  in  a  way  analogous  to  that  by  which  the  en- 
tire organism  is  qualitatively  differentiated  from  things 
around   it.  Evidently   this   selective   assimilation 

illustrates  the  general  truth,  demonstrable  a  priori,  that  like 
units  tend  to  segregate.  It  illustrates,  moreover,  the  further 
aspect  of  this  general  truth,  that  the  pre-existence  of  a  mass 
of  certain  units,  produces,  probably  by  polar  attraction,  a 
tendency  for  diffused  units  of  the  same  kind  to  aggregate 
with  this  mass,  rather  than  elsewhere.  It  has  been  shown  of 
particular  salts,  A  and  B,  co-existing  in  a  solution  not  suf- 
ficiently concentrated  to  crystallize,  that  if  a  crystal  of  the  salt 
A  be  put  in  o  the  solution,  it  will  increase  by  uniting  with  itself 
the  dissolved  atoms  of  the  salt  A  ;  and  that  similarly,  though 
there  otherwise  takes  place  no  deposition  of  the  salt  B,  yet  if 
a  crystal  of  the  salt  B  is  placed  in  the  solution,  it  will  exercise 
a  coercive  force  on  the  diffused  atoms  of  this  salt,  and  grow  at 
their  expense.  No  doubt  much  organic  assimilation  occurs 
in  the  same  way.  Particular  parts  of  the  organism  are  com- 
posed of  special  units,  or  have  the  function  of  secretin" 
special  units,  which  are  ever  present  in  them  in  large  quan- 


152  THE    INDUCTIONS    OF    BIOLOGY. 

tities.  The  fluids  circulating  through  the  body  contain 
special  units  of  this  same  order.  And  these  diffused  units 
are  continually  being  deposited  along  with  the  groups  of  like 
units  that  already  exist.  How  purely  physical  are  the  causes 
of  this  selective  assimilation,  is,  indeed,  conclusively  shown 
"by  the  fact,  that  abnormal  constituents  of  the  blood  are 
segregrated  in  the  same  way.  Cancer-cells  having  begun  to 
be  deposited  at  a  particular  place,  continue  to  be  deposited  at 
that  place.  Tubercular  matter,  making  its  appearance  at 
particular  points,  collects  more  and  more  round  those  points. 
And  similarly  in  numerous  pustular  diseases.  Where 

the  component  units  of  an  organ,  or  some  of  them,  do  not 
exist  as  such  in  the  circulating  fluids,  but  are  formed  out  of 
elements  or  compounds  that  exist  separately  in  the  circulat- 
ing fluids ;  it  is  clear  that  the  process  of  differential  assimil- 
ation is  of  a  more  complex  kind.  Still,  however,  it  seems 
not  impossible  that  it  is  carried  on  in  an  analogous  way.  If 
there  be  an  aggregate  of  compound  atoms,  each  of  which 
contains  the  constituents  A,  B,  C  ;  and  if  round  this  aggre- 
gate the  constituents  A  and  B  and'  C  are  diffused  in  uncom- 
bined  states ;  it  may  be  suspected  that  the  coercive  polar  force 
of  these  aggregated  compound  atoms  A,  B,  C,  may  not  only 
bring  into  union  with  themselves  adjacent  compound  atoms 
A,  B,  C,  but  may  cause  the  adjacent  constituents  A  and  B 
and  C  to  unite  into  such  compound  atoms,  and  then  aggre- 
gate with  the  mass.  Should  this  be  so,  the  process  of  differ- 
ential assimilation,  which  plays  so  important  a  part  in 
organic  development,  will  not  be  difficult  to  understand.  At 
present,  however,  chemical  inquiry  appears  to  have  furnished 
no  evidence  either  for  or  against  such  an  hypothesis. 


CHAPTER   III. 

FUNCTION. 

§  55.  Does  Structure  originate  Function,  or  docs  Func- 
tion originate  Structure  ?  is  a  question  about  which  there  has 
been  disagreement.  Using  the  word  Function  in  its  widest 
signification,  as  the  totality  of  all  vital  actions,  the  question 
amounts  to  this — does  Life  produce  Organization,  or  does 
Organization  produce  Life  ?  ^ 

To  answer  this  question  is  not  easy,  since  we  habitually 
find  the  two  so  associated  that  neither  seems  possible  without 
the  other ;  and  they  appear  uniformly  to  increase  and 
decrease  together.  If  it  be  said  that  the  arrangement  of  or- 
ganic substances  in  particular  forms,  cannot  be  the  ultimate 
cause  of  vital  changes,  which  must  depend  on  the  properties 
of  such  substances  ;  it  may  be  replied  that,  in  the  absence  of 
structural  arrangements,  the  forces  evolved  cannot  be  so 
directed  and  combined  as  to  secure  that  correspondence 
between  inner  and  outer  actions  which  constitutes  Life. 
Again,  to  the  allegation  that  the  vital  activity  of  every  germ 
whence  an  organism  arises,  is  obviously  antecedent  to  the 
development  of  its  structures ;  there  is  the  answer  that  such 
germ  is  not  absolutely  structureless,  but  consists  of  a  mass  of 
cells,  containing  a  cell  that  differs  from  the  rest,  and  initiates 
the  developmental  changes.  There  is,  however,  one 

fact  implying  that  Function  must  be  regarded  as  taking  pre- 
cedence of  Structure.  Of  the  lowest  Ehizopods,  which  pre- 
11 


154  THE    INDUCTIONS  ^F    BIOLOGY. 

sont  no  distinctions  of  parts,  and  nevertheless  feed  and 
grow  and  move  about,  Prof.  Huxley  has  remarked  that  they 
exhibit  Life  without  Organization.  The  perpetual  changes  of 
form  which  alone  distinguish  one  of  these  creatures  from  an 
inanimate  fragment,  are  no  doubt  totally  irregular  and  un- 
directed. Still  they  do,  through  an  average  of  accidents, 
subserve  the  creatures'  nutrition ;  and  they  do  imply  an  ex- 
penditure of  force  that  in  some  way  depends  on  the  consump- 
tion of  nutriment.  They  do,  therefore,  though  in  the  rudest 
way,  display  a  vital  adjustment  of  internal  to  external  relations. 

§  56.  Function  falls  into  divisions  of  several  kinds,  ac- 
cording to  our  point  of  view.  Let  us  take  these  divisions  in 
the  order  of  their  simplicity. 

Under  Function  in  its  widest  sense,  are  included  both  the 
statical  and  the  dynamical  distributions  of  force  which  an 
organism  opposes  to  the  forces  brought  to  bear  on  it.  In  a 
tree,  the  woody  core  of  trunk  and  branches,  and  in  an  animal, 
the  skeleton,  internal  or  external,  may  be  regarded  as  pas- 
sively resisting  the  gravity  and  momentum  which  tend 
habitually  or  occasionally  to  derange  the  requisite  relations 
between  the  organism  and  its  environment ;  and  since  they 
resist  these  forces  simply  by  their  cohesion,  their  functions 
may  be  classed  as  statical.  Conversely,  the  leaves  and  sap- 
vessels  in  a  tree,  and  those  organs  which  in  an  animal 
similarly  carry  on  nutrition  and  circulation,  as  well  as  those 
which  generate  and  direct  muscular  motion,  must  be  con- 
sidered as  dynamical  in  their  actions.  From  another 
point  of  view,  Function  is  divisible  into  the  accumulation  of 
force  (latent  in  food)  ;  the  expenditure  of  force  (latent  in  the 
tissues  and  certain  matters  absorbed  by  them)  ;  and  the 
transfer  of  force  (latent  in  the  prepared  nutriment  or  blood) 
from  the  parts  which  accumulate  to  the  parts  which  expend. 
In  plants  we  see  little  beyond  the  first  of  these  :  expenditure 
being  inappreciable,  and  transfer  required  only  to  facilitate 


FUNCTION.  155 

accumulation.  In  animals,  the  function  of  accumulation 
comprehends  those  processes  by  which  the  materials  contain- 
ing latent  force  are  taken  in,  digested,  and  separated  from 
other  materials  ;  the  function  of  transfer  comprehends  those 
processes  by  which  these  materials,  and  such  others  as  are 
needful  to  liberate  the  forces  they  contain,  are  conveyed 
throughout  the  organism ;  and  the  function  of  expenditure 
comprehends  those  processes  by  which  the  forces  are  liberated 
from  these  materials,  and  transformed  into  properly  co-ordin- 
ated motions.  Each  of  these  three  most  general 
divisions,  includes  several  more  special  divisions.  The  accu- 
mulation of  force  may  be  separated  into  alimentation  and 
aeration ;  of  which  the  first  is  again  separable  into  the 
various  acts  gone  through  between  prehension  of  food  and 
the  transformation  of  part  of  it  into  blood.  By  the  transfer 
of  force  is  to  be  understood  what  we  call  circulation;  if  the 
meaniu":  of  circulation  be  extended  to  embrace  the  duties  of 
both  the  vascular  system  and  the  lymphatics.  Under  the 
head  of  expenditure  of  force,  come  nervous  actions  and  mus- 
cular actions :  though  not  absolutely  co-extensive  with  ex- 
penditure, these  are  almost  so.  Lastly,  there  are  the 
subsidiary  functions  which  do  not  properly  fall  within  any 
of  these  general  functions,  but  subserve  them  by  removing 
the  obstacles  to  their  performance  :  those,  namely,  of  ex- 
cretion and  exhalation,  whereby  waste  products  are  got 
rid  of.  Again,  disregarding  their  purposes  and 
considering  them  analytically,  the  general  physiologist  may 
consider  functions  in  their  widest  sense  as  the  correlatives  of 
tissues — the  actions  of  epidemic  tissue,  cartilaginous  tissue, 
elastic  tissue,  connective  tissue,  osseous  tissue,  muscular 
tissue,  nervous  tissue,  glandular  tissue.  Once  more, 
plrysiology  in  its  concrete  interpretations,  recognizes  special 
functions  as  the  ends  of  special  organs — regards  the  teeth  as 
having  the  office  of  mastication  ;  the  heart  as  an  apparatus 
to  propel  blood  ;  this  gland  as  fitted  to  produce  one  requisite 


156  THE    [EDUCTIONS    OF    BIOLOGY. 

secretion  and  that  to  produce  another ;  each  muscle  as  the 
agent  of  a  particular  motion  ;  each  nerve  as  the  vehicle  of  a 
special  sensation  or  a  special  motor  impulse. 

It  is  clear  that  dealing  with  Biology  only  in  its  larger 
aspects,  specialities  of  function  do  not  concern  us ;  except  in 
so  far  as  they  serve  to  illustrate,  or  to  qualify,  its  general- 
ities 

§  57.  The  first  induction  to  be  here  set  down,  is  a 
familiar  and  obvious  one :  the  induction,  namely,  that  com- 
plexity of  function,  is  the  correlative  of  complexity  of  struc- 
ture. The  leading  aspects  of  this  truth  must  be  briefly  noted. 

Where  there  are  no  distinctions  of  structure,  there  are  no 
distinctions  of  function.  One  of  the  Rhizopods  above 
instanced  as  exhibiting  life  without  organization,  will  serve 
as  an  illustration.  From  the  outside  of  this  creature, 
which  has  not  even  a  limiting  membrane,  there  are  protruded 
numerous  thread-like  processes.  Originating  from  any  point 
of  the  surface,  each  of  these  may  contract  again  and  disap- 
pear ;  or  it  may  touch  some  fragment  of  nutriment,  which  it 
draws  with  it,  when  contracting,  into  the  general  mass — thus 
serving  as  hand  and  mouth  ;  or  it  may  come  in  contact  with 
its  fellow-processes  at  a  distance  from  the  body,  and  become 
confluent  with  them  ;  or  it  may  attach  itself  to  an  adjacent 
fixed  object,  and  help  by  its  contraction  to  draw  the  body 
into  a  new  position.  In  brief,  this  structureless  speck  of 
animated  jelly,  is  at  once  all  stomach,  all  skin,  all  mouth,  all 
limb,  and  doubtless,  too,  all  lung.  In  organisms 

having  a  fixed  distribution  of  parts,  there  is  a  concomitant 
fixed  distribution  of  actions.  Among  plants  we  see  that 
when,  instead  of  a  uniform  tissue  like  that  of  the  Algce, 
everywhere  devoted  to  the  same  process  of  assimilation, 
there  arise,  as  in  the  Exogens,  root  and  stem  and  leaves, 
there  arise  correspondingly  unlike  processes.  Still  more  con- 
spicuously among  animals,  do  there  result  varieties  of  function 
when  the  originally  homogeneous  mass  is  replaced  by  hetero- 


FUNCTION.  157 

geneous  organs;  since  both  singly  and  by  their  combinations, 
do  modified  parts  generate  modified  changes.  Up  to 

the  highest  organic  types,  this  dependence  continues  mani- 
fest ;  and  it  may  be  traced  not  only  under  this  most  general 
form,  but  also  under  the  more  special  form,  that  in  animals 
having  one  set  of  functions  developed  to  more  than  usual 
heterogeneity,  there  is  a  correspondingly  heterogeneous  ap- 
paratus devoted  to  them.  Thus  among  birds,  which  have 
more  varied  locomotive  powers  than  mammals,  the  limbs  are 
more  widely  differentiated  ;  while  mammals,  which  rise  to 
more  numerous  and  more  involved  adjustments  of  inner  to 
outer  relations  than  birds,  have  more  complex  nervous 
systems. 

§  58.  It  is  a  generalization  almost  equally  obvious  with 
the  last,  that  functions,  like  structures,  arise  by  progressive 
differentiations.  Just  as  an  organ  is  first  an  indefinite  rudi- 
ment, having  nothing  but  some  most  general  characteristic 
in  common  with  the  form  it  is  ultimately  to  take ;  so  a 
function  begins  as  a  kind  of  action  that  is  like  the  kind  of 
action  it  will  eventually  become,  only  in  a  very  vague  way. 
And  in  functional  development,  as  in  structural  development, 
the  leading  trait  thus  early  manifested,  is  followed  success- 
ively by  traits  of  less  and  less  importance  This  holds 
equally  throughout  the  ascending  grades  of  organisms,  and 
throughout  the  stages  of  each  organism.  Let  us  look  at 
cases :  confining  our  attention  to  animals,  in  which  func- 
tional development  is  better  displayed  than  in  plants 

The  first  differentiation  established,  separates  the  two 
fundamentally- opposed  functions  above  named — the  accumu- 
lation of  force  and  the  expenditure  of  force.  Passing  over 
the,  (Protozoa  among  which,  however,  such  tribes  as  present 
fixed  distributions  of  parts  show  us  substantially  the  same 
thing),  and  commencing  with  the  lowest  Coelentcrata,  where 
definite  tissues  make  their  first  appearance,  we  observe  that 
the  onlv  marked  functional  distinction  is  between  the  endo- 


15^  THfl    IXTTUCTTONS    OF    RIOT.OCt. 

derm,  which  absorbs  nutriment,  and  the  ectoderm,  which,  i»y 
its  own  contractions  and  those  of  the  tentacles  it  bears,  pro- 
duces motion.  That  the  functions  of  accumulation  and  ex- 
penditure are  here  very  incompletely  distinguished,  may  be 
admitted  without  affecting  the  position  that  this -is  the  first 
specialization  which  begins  to  appear.  These  two 

most  genei'al  and  most  radically-opposed  functions,  become, 
in  the  Pohjzoa,  much  more  clearly  marked-off  from  each 
other  ;  at  the  same  time  that  each  of  them  becomes  partially 
divided  into  subordinate  functions.  The  endoderm.  and 
ectoderm  are  no  longer  merely  the  inner  and  outer  walls  of 
the  same  simple  sac  into  which  the  food  is  drawn  ;  but  the 
endoderm  forms  a  true  alimentary  canal,  separated  from  the 
ectoderm  by  a  peri- visceral  cavity,  containing  the  nutritive 
matters  absorbed  from  the  food.  That  is  to  say,  the  function 
of  accumulating  force  is  exercised  by  a  part  distinctly  divided 
from  the  part  mainly  occupied  in  expending  force :  the 
space  between  them,  full  of  absorbed  nutriment,  effecting  in 
a  vague  way  that  transfer  of  force  which,  at  a  higher  stage  of 
evolution,  becomes  a  third  leading  function.  Meanwhile,  the 
endoderm  no  longer  discharges  the  accumulative  function 
in  the  same  way  throughout  its  whole  extent ;  but  its  differ- 
ent portions,  oesophagus,  stomach  and  intestine,  perform 
different  portions  of  this  function.  And  instead  of  a  con- 
tractility uniformly  diffused  through  the  ectoderm,  there 
have  arisen  in  it,  some  parts  which  have  the  office  of  con- 
tracting (muscles),  and  some  parts  which  have  the  office  of 
making  them  contract  (nerves  and  ganglia).  As  we 

pass  upwards,  the  transfer  of  force,  hitherto  effected  quite 
incidentally,  comes  to  have  a  special  organ.  In  the  ascidian 
molluscs,  circulation  is  produced  by  a  muscular  tube,  open  at 
both  ends,  which,  by  a  wave  of  contraction  passing  along  it, 
sends  out  at  one  end  the  nutrient  fluid  drawn  in  at  the 
other  ;  and  which,  having  thus  propelled  the  fluid  for  a  time 
in  one  direction,  reverses  its  movement  and  propels  it  in  the 
opposite  direction.      By  such   means   does  this  rudimentary 


FUNCTION.  159 

heart  generate  alternating  currents  in  the  crude  and  dilute 
nutriment  occupying  the  peri-visceral  cavity.  How  the  func- 
tion of  transferring  force,  thus  vaguely  indicated  in  these  in- 
ferior forms,  comes  afterwards  to  be  the  definitely-separated 
office  of  a  complicated  apparatus  made  up  of  many  parts,  each 
of  which  has  a  particular  portion  of  the  general  duty,  need 
not  be  described.  It  is  sufficiently  manifest  that  this  General 
function  becomes  more  clearly  marked-off  from  the  others, 
at  the  same  time  that  it  becomes  itself  Darted  into  subordinate 
tunctions 

In  a  developing  emDrvo,  tne  functions  or  more  strictly 
the  structures  whicn  are  to  perform  tnem,  arise  in  the  same 
general  order.  A  like  primarv  distinction  very  early  ap- 
pears between  the  endoderm  and  the  ectoderm — the  part 
which  has  the  office  of  accumulating  force,  and  the  part  out 
jf  which  grow  those  organs  that  are  the  great  expenders  of 
force  Between  these  two  there  presently  becomes  visible 
the  rudiment  of  that  vascular  system,  which  has  to  fulfil  the 
intermediate  duty  of  transferring  force.  Of  these  three 
general  functions,  that  of  accumulating  force  is  carried  on 
fi-om  the  outset:  the  endoderm,  even  while  yet  incompletely 
differentiated  from  the  ectoderm,  absorbs  nutritive  matters 
from  the  subjacent  yelk.  The  tr?,nsfer  of  force  is  also  to 
some  extent  effected  by  the  rudimentary  vascular  system,  as 
soon  as  its  central  cavity  and  attached  vessels  are  sketched 
out  But  the  expenditure  of  force  (in  the  higher  animals  at 
least)  is  not  appreciably  displayed  by  the  ectodermic  struc- 
tures that  are  afterwards  to  be  mainly  devoted  to  it :  there 
is  no  sphere  for  the  actions  of  these  parts.  Similarly 

with  the  chief  subdivisions  of  these  fundamental  functions. 
If  we  look  at  those  discharged  by  the  ectoderm,  potentially 
if  not  actually,  we  see  that  the  distinction  first  established 
separates  the  office  of  transforming  other  force  into  mechani 
cal  motion,  from  the  office  of  liberating  the  force  to  be  so 
transformed — in  the  midst  of  the  part  out  of  which  the  mus- 
cular system   is  to    be  developed,  there  is  marked-out  the 


160  THE    INDUCTIONS    OF    BIOLOGY. 

rudiment  of  the  nervous  system.  This  indication  of  struc- 
tures which  are  to  share  between  them  the  general  duty  oi 
expending  force,  is  soon  followed  by  changes  that  foreshadow 
further  specializations  of  this  general  duty.  In  the  incipient 
nervous  system,  there  begins  to  arise  that  contrast  betweeu 
the  cerebral  mass  and  the  spinal  cord,  which,  in  the  main, 
answers  to  the  division  of  nervous  actions  into  directive 
and  executive ;  and  at  the  same  time,  the  appearance  of 
vertebral  laminre  foreshadows  the  separation  of  the  osseous 
system,  which  has  to  resist  the  strains  of  muscular  action, 
from  the  muscular  system,  which,  in  generating  motion,  en- 
tails these  strains.  Simultaneously  there  have  been  going 
on  similar  actual  and  potential  specializations  in  the  functions 
of  accumulating  force  and  transferring  force.  And  through- 
out all  subsequent  phases,  the  method  is  substantially  the 
same. 

This  progress  from  general,  indefinite,  and  simple  kinds 
of  action,  to  special,  definite,  and  complex  kinds  of  action, 
has  been  aptly  termed  by  Milne-Edwards,  the  "  physio- 
logical division  of  labour."  Perhaps  no  metaphor  can  more 
truly  express  the  nature  of  this  advance  from  vital  activity 
in  its  lowest  forms  to  vital  activity  in  its  highest  forms. 
And  probably  the  general  reader  cannot  in  any  other  way 
obtain  so  clear  a  conception  of  functional  development  in 
organisms,  as  he  can  by  tracing  out  functional  development  in 
societies  :  noting  how  there  first  comes  a  distinction  between 
the  governing  class  and  the  governed  class ;  how  while  in 
the  governing  class  there  slowly  grow  up  such  differences  of 
duby  as  the  civil,  military,  and  ecclesiastical,  there  arise  in 
the  governed  class,  fundamentally  industrial  differences  like 
those  between  agriculturists  and  artizans ;  and  how  there  is 
a  continual  multiplication  of  such  specialized  occupations, 
and  specialized  shares  of  each  occupation. 

§  59.  Fully  to  understand  this  change  from  homogeneity 
to  heterogeneity  of  function,  which  accompanies  the  change 


FUNCTION.  161 

from  homogeneity  to  heterogeneity  of  structure,  it  is  needful 
to  contemplate  it  under  a  converse  aspect.  Standing  alone, 
the  above  exposition  conveys  both  an  inadequate  and  an 
erroneous  idea.  The  divisions  and  subdivisions  of  function, 
becoming  definite  as  they  become  multiplied,  do  not  lei.d  to 
a  more  and  more  complete  independence  of  functions  ;  as 
they  would  do  were  the  process  nothing  beyond  that  just  de- 
scribed ;  but  by  a  simultaneous  process  they  are  rendered 
more  mutually  dependent.  While  in  one  respect  they  are 
separating  from  each  other,  they  are  in  another  respect  com- 
bining with  each  other.  At  the  same  time  that  they  are 
bein^  differentiated,  they  are  also  being  integrated.  Some 
illustrations  will  make  this  plain. 

In  animals  which  display  little  beyond  the  primary  dif- 
ferentiation of  functions,  the  activity  of  that  part  which 
absoi'bs  nutriment  or  accumulates  force,  is  not  immediately 
bound  up  with  the  activity  of  that  part  which,  in  producing 
motion,  expends  force.  In  the  higher  animals,  however,  the 
performance  of  the  alimentary  functions  depends  on  the  per- 
formance of  various  muscular  and  nervous  functions.  Masti- 
cation and  swallowing  are  nervo-muscular  acts ;  the  ryth- 
mical contractions  of  the  stomach  and  the  allied  vermicular 
motions  of  the  intestines,  result  from  the  stimulation  of  cer- 
tain muscular  coats  by  the  nerve- fibres  distributed  through 
them  ;  the  secretion  of  the  several  digestive  fluids  by  their 
respective  glands,  is  due  to  nervous  excitation  of  them ;  and 
digestion,  besides  requiring  these  special  aids,  is  not  properly 
performed  in  the  absence  of  a  continuous  discharge  of  energy 
from  the  great  nervous  centres.  Again,  the  function 

of  transferring  nutriment  or  latent  force,  from  part  to  part, 
though  at  first  not  closely  connected  with  the  other  functions, 
eventually  becomes  so.  The  short  contractile  tube  which 
propels  backwards  and  forwards  the  crude  dilute  blood  con- 
tained in  the  perivisceral  cavity  of  an  inferior  mollusc,  is 
neither  structurally  nor  functionally  much  entangled  with 
the  creature's  other  organs.    But  on  passing  upwards  through 


162  THE    INDUCTIONS    OV    BIOLOGY 

the  higher  molluscs,  in  which  this  simple  tube  is  replaced 
Ly  a  system  of  branched  tubas,  that  deliver  their  contents 
through  their  open  ends  into  the  tissues  at  distant  parts ; 
and  on  coming  to  those  advanced  types  of  animals  which 
have  closed  arterial  and  venous  systems,  ramifying  minutely 
in  every  corner  of  ever}'  organ ;  we  find  that  the  vascular 
apparatus,  while  it  has  become  structurally  interwoven 
with  the  whole  body,  has  become  unable  to  fulfil  its 
office  without  the  help  of  offices  that  are  quite  separated  from 
its  own.  The  heart  is  now  a  complex  pump,  worked  by 
powerful  muscles  that  are  excited  by  a  local  nervous  system  ; 
and  the  general  nervous  system  also,  takes  a  share  in  regu- 
lating the  contractions  both  of  the  heart  and  of  all  the 
arteries.  On  the  due  discharge  of  the  respiratory  function, 
too,  the  function  of  circulation  is  directly  dependent :  if  the 
aeration  of  the  blood  is  impeded,  the  vascular  activity  is 
lowered  ;  and  arrest  of  the  one  very  soon  causes  stoppage  of 
the  other.  Similarly  with  the  duties  of  the  nervo- 

muscular  system.  Animals  of  low  organization,  in  which 
the  differentiation  and  integration  of  the  vital  actions  have 
not  been  carried  far,  will  move  about  for  a  considerable  time 
after  being  eviscerated,  or  deprived  of  those  appliances  by 
which  force  is  accumulated  and  transferred.  But  animals  of 
high  organization  are  instantly  killed  by  the  removal  of 
these  appliances,  and  even  by  the  injury  of  minor  parts  of 
them  :  a  dog's  movements  are  suddenly  brought  to  an  end,  by 
cutting  one  of  the  main  canals  along  which  the  materials 
that  evolve  movements  are  conveyed.  Thus  while 

in  well-developed  creatures  the  distinction  of  functions  is 
very  marked,  the  combination  of  functions  is  very  close. 
From  instant  to  instant,  the  aeration  of  blood  implies  that, 
certain  respiratory  muscles  are  being  made  to  contract  by 
certain  nerves;  and  that  the  heart  is  duly  propelling  the 
blood  to  be  aerated.  From  instant  to  instant  digestion  pro- 
ceeds only  on  condition  that  there  is  a  supply  of  aerated  blood, 
and  a  due  current  of  nervous  energy  through  the  digestive 


FUNCTION.  .103 

organs.  That  the  heart  may  act,  it  must  from  instant  to  in- 
stant be  excited  by  discharges  from  certain  ganglia ;  and 
the  discharges  from  these  ganglia  are  made  possible,  only  by 
the  conveyance  to  them,  from  instant  to  instant,  of  the 
blood  which  ttifj  heart  propels. 

It  is  not  easy  to  find  an  adequate  expression  for  this  double 
re-distribution  of  functions.  It  is  not  easy  to  realize  a  trans- 
formation through  which  the  functions  thus  become  in  one 
sense  separated  and  in  another  sense  combined,  or  even  in- 
terfused. Here,  however,  as  before,  an  analogy  drawn  from 
social  organization  helps  us.  If  we  observe  how  the  increas- 
ing division  of  labour  in  societies,  is  accompanied  by  a  closer 
co-operation  ;  and  how  the  agencies  of  different  social  actions, 
while  becoming  in  one  respect  more  distinct,  become  in  an- 
other respect  more  minutely  ramified  through  each  other ; 
we  shall  understand  better  the  increasing  physiological  co- 
operation that  accompanies  increasing  physiological  division 
of    labour.  Note,    for  example,    that   while   local 

divisions  and  classes  of  the  community  have  been  grow- 
ing unlike  in  their  several  occupations,  the  carrying  on  of 
their  several  occupations  has  been  growing  dependent  on 
♦.he  due  activity  of  that  vast  organization  by  which  sus- 
tenance is  collected  and  diffused.  During  the  early  stages 
of  social  development,  every  small  group  of  people,  and  often 
every  family,  obtained  separately  its  own  necessaries;  but 
now,  for  each  necessary,  and  for  each  superfluity,  there  ex- 
ists a  combined  body  of  wholesale  and  retail  distributors, 
which  brings  its  branched  channels  of  supply  within  reach 
of  all.  While  each  citizen  is  pursuing  a  business  that  does  not 
immediately  aim  at  the  satisfaction  of  his  personal  wants,  his 
personal  wants  are  satisfied  by  a  general  agency  that  brings 
from  all  places  commodities  for  him  and  his  fellow-citizens 
— an  agency  which  could  not  cease  its  special  duties  for  a  few 
days,  without  bringing  to  an  end  his  own  special  duties  and 
those  of  most  others.  Consider,  again,  how  each 

of  these  differentiated  functions  is  everywhere  pervaded  by 


164  THE    INDUCTIONS   OF    BIOLOGY. 

certaiD  otlicr  differentiated  functions.  Merchants,  manu- 
facturers, wholesale  distributors  of  their  several  species,  to- 
gether with  lawyers,  bankers,  &c,  all  employ  clerks.  In 
clerks  we  have  a  specialized  class  dispersed  through  various 
other  classes  ;  and  having  its  function  fused  with  the  differ- 
ent functions  of  these  various  other  classes.  Similarly 
commercial  travellers,  though  having  in  one  sense  a 
separate  occupation,  have  in  another  sense  an  occupation 
forming  part  of  each  of  the  many  occupations  which  it 
aids.  As  it  is  here  with  the  sociological  division 

of  labour,  so  is  it  with  the  physiological  division  of  la- 
bour above  described.  Just  as  we  see  in  an  advanced  com- 
munity, that  while  the  magisterial,  the  clerical,  the  medical, 
the  legal,  the  manufacturing,  and  the  commercial  activities, 
have  grown  distinct,  theyJiave  yet  their  agencies  mingled 
together  in  every  locality ;  so  in  a  developed  organism,  we 
see  that  while  the  general  functions  of  circulation,  secretion, 
absorption,  excretion,  contraction,  excitation,  &c,  have  be- 
come differentiated,  yet  through  the  ramifications  of  the  sys- 
tems apportioned  to  them,  they  are  closely  combined  with 
each  other  in  every  organ. 

§  60.  The  physiological  division  of  labour,  is  usually  not 
carried  so  far  as  wholly  to  destroy  the  primary  physiological 
community  of  labour.  As  in  societies  the  adaptation  of  special 
classes  to  special  duties,  does  not  entirely  disable  these  classes 
from  performing  each  others'  duties  on  an  emergency ;  so  in 
organisms,  tissues  and  structures  that  have  become  fitted  to 
the  particular  offices  they  have  ordinarily  to  discharge,  often 
remain  partially  able  to  discharge  other  offices.  It  has  been 
pointed  out  by  Dr  Carpenter,  that  "  in  cases  where  the  differ 
ent  functions  are  highly  specialized,  the  general  structure 
retains,  more  or  less,  the  primitive  community  of  function 
which  originally  characterized  it."  A  few  instances  will 
bring  home  this  generalization. 

The  roots  and    leaves    of  plants    are   widely   differenti- 


FUNCTION.  18a 

ated  in  their  functions :  by  the  roots,  water  and  mineral 
substances  are  absorbed ;  while  the  leaves  take  in.  and  de- 
compose, carbonic  acid.  Nevertheless,  leaves  retain  a  con- 
siderable power  of  absorbing  water  ;  and  in  what  are  popu- 
larly called  "  air-plants,"  the  absorption  of  water  is  wholly 
carried  on  by  them  and  by  the  stems.  Conversely,  the  under- 
ground parts  can  partially  assume  the  functions  of  leaves  : 
the  exposed  tuber  of  a  potato  develops  chlorophyll  on  its 
surface,  and  in  other  cases,  roots,  properly  so  called,  do  the 
like.  In  trees,  the  trunks,  which  have  in  great  measure 
ceased  to  produce  buds,  recommence  producing  them  if  the 
branches  are  cut  off;  and  under  such  circumstances  the 
roots,  though  not  in  the  habit  of  developing  leaf-bearing 
organs,   send   up  numerous   suckers.  Much   more 

various  examples  of  vicarious  function  may  be  found  among 
animals.  Starting  with  the  extreme  case  of  the  common 
hydra,  which  can  live  when  the  duties  of  skin  and  stomach 
have  been  interchanged  by  turning  it  inside  out,  we  find  in 
all  grades,  even  up  to  the  highest,  that  absorbent  and  excret- 
ing organs  can  partially  supply  each  others'  places.  Among 
well-organized  animals,  the  taking  in  of  nutriment  is  ef- 
fected exclusively  by  an  internal  membrane  ;  but  the  external 
membrane  is  not  wholly  without  the  power  to  take  in  nutri- 
ment :  when  food  cannot  be  swallowed,  life  may  be  pro- 
longed by  immersing  the  body  in  nutritive  fluids.  The  ex- 
cretion of  carbonic  acid  and  absorption  of  oxygen,  are  mainly 
performed  by  the  lungs,  in  creatures  which  have  lungs  ;  but 
in  such  creatures  there  continues  a  certain  amount  of  cutane- 
ous respiration,  and  in  soft-skinned  batrachians  like  the  frog, 
this  cutaneous  respiration  is  important.  Again,  when  the 
kidneys  are  not  discharging  their  duties,  a  notable  quantity 
of  urea   is    got   rid   of    by   perspiration.  Other 

instances  are  supplied  by  the  higher  functions.  In  man, 
the  limbs,  which  among  lower  vertebrates  are  almost  wholly 
organs  of  locomotion,  are  specialized  into  organs  of  locomo- 
tion and  organs  of  manipulation.     Nevertheless,  the  human 


166 


THE    INDUCTIONS    OF    I IOLOGY. 


arms  and  legs  do,  when  needful,  fulfil,  to  some  extent,  each 
others'  offices.  JSot  only  in  childhood  and  old  age  are  the 
arms  used  for  purposes  of  support,  but  on  occasions  of  emerg- 
ency, as  when  mountaineering,  they  are  so  used  by  men  in  full 
vigour.  And  that  legs  are  to  a  considerable  degree  capable 
of  performing  the  duties  of  arms,  is  proved  by  the  great 
amount  of  manipulatory  skill  reached  by  them  when  the 
arms  are  absent.  Among  the  perceptions,  too,  there  are  ex- 
amples of  partial  substitution.  The  deaf  Dr  Kitto  described 
himself  as  having  become  excessively  sensitive  to  vibrations 
propagated  through  the  body ;  and  as  so  having  gained  the 
power  of  perceiving,  through  his  general  sensations,  those 
neighbouring  concussions  of  which  the  ears  ordinarily  give 
notice.  Blind  people  make  hearing  perform,  in  part,  the 
office  of  vision.  Instead  of  identifying  the  positions  and 
sizes  of  neighbouring  objects  by  the  reflection  of  light  from 
their  surfaces,  they  do  this  in  a  rude  way  by  the  reflection 
of  sound  from  their,  surfaces. 

We  see,  as  we  might  expect  to  see,  that  this  power  of  per- 
forming more  general  functions,  is  great  in  proportion  as 
the  parts  have  been  but  little  adapted  to  their  special  func- 
tions. In  the  hydra,  where  complete  transposition  of  functions 
is  possible,  the  histological  differentiation  that  has  been  estab- 
lished, is  extremely  slight,  or  even  inappreciable.  Those  parts 
of  plants  which  show  so  considerable  a  power  of  discharging 
each  others'  offices,  are  not  widely  unlike  in  their  minute 
structures.  And  the  tissues  that  in  animals  are  to  some 
extent  mutually  vicarious,  are  tissues  in  which  the  original 
cellular  composition  is  still  conspicuous.  But  we  do  not  find 
evidence  that  the  muscular,  nervous,  or  osseous  tissues  are 
able  in  any  degree  to  perform  those  processes  which  the 
less  differentiated  tissues  perform.  Nor  have  we  any 
proof  that  nerve  can  partially  fulfil  the  duty  of  muscle, 
or  muscle  that  of  nerve.  "We  must  say,  therefore,  that 
the  ability  to  resume  the  primordial  community  of  function 


FUNCTION.  167 

varies  inversely  as  the  established  specialization  of  function  ; 
and  that  it  disappears  when  the  specialization  of  function 
becomes  great. 

§  GL.  Something  approaching  to  a  priori  reasons  may  be 
given  for  the  conclusions  thus  reached  a  posteriori.  They 
must  be  accepted  for  as  much  as  they  seem  worth. 

It  may  be  argued  that  on  the  hypothesis  of  Evolution, 
Life  necessarily  comes  before  organization.  On  this  hypo- 
thesis, organic  matter  in  a  state  of  homogeneous  aggregation, 
must  precede  organic  matter  in  a  state  of  heterogeneous  ag- 
gregation. But  since  the  passing  from  a  structureless  state 
to  a  structured  state,  is  itself  a  vital  process,  it  follows  that 
vital  activity  must  have  existed  while  there  was  yet  no 
structure  :    structure   could   not  else   arise.  That 

function  takes  precedence  of  structure,  seems  also  implied  in 
the  definition  of  Life.  If  Life  consists  of  inner  actions  so 
adjusted  as  to  balance  outer  actions — if  the  actions  are  the 
substance  of  Life,  while  the  adjustment  of  them  constitutes 
its  form;  then,  may  we  not  say  that  the  actions  to  be  formed 
must  come  before  that  which  forms  them — that  the  continu- 
ous change  which  is  the  basis  of  function,  must  come  before 
the  structure  which  brings  function  into  shape  ?  Or 

again,  since  throughout  all  phases  of  Life  up  to  the  highest, 
every  advance  is  the  effecting  of  some  better  adjustment  of 
inner  to  outer  actions;  and  since  the  accompanying  new  com- 
plexity of  structure  is  simply  a  means  of  making  possible 
this  better  adjustment ;  it  follows  that  function  is  from 
beginning  to  end  the  determining  cause  of  structure.  ]Not 
only  is  this  manifestly  true  where  the  modification  of  struc- 
ture arises  by  reaction  from  modification  of  function  ;  but  it 
is  also  true  where  a  modification  of  structure  otherwise  pro- 
duced, apparently  initiates  a  modification  of  function.  For 
it  is  only  when  such  so-called  spontaneous  modification  of 
structure  subserves  some  advantageous  action,  that  it  is  per- 


per- 


168  THE   INDUCTIONS    DF   BIOLOGY. 

manently  established  :  if  it  is  a  structural  modification  that 
hajypens  to  facilitate  the  vital  activities,  "natural  selection" 
retains  and  increases  it ;  but  if  not,  it  disappears. 

The  connexion  which  we  noted  between  heterogeneity 
of  structure  and  heterogeneity  of  function — a  connexion 
made  so  familiar  by  experience  as  to  appear  scarcely  worth 
specifying — is  clearly  a  necessary  one.  It  follows  from  the 
general  truth  that  in  proportion  to  the  heterogeneity  of  any 
aggregate,  is  the  heterogeneity  it  will  produce  in  any  inci- 
dent force  (First  Principles,  §  116).  The  force  continually 
liberated  in  the  organism  by  decomposition,  is  here  the  inci- 
dent force ;  the  functions  are  the  variously  modified  forms 
produced  in  its  divisions  by  the  organs  they  pass  through  ; 
and  the  more  multiform  the  organs  the  more  multiform  must 
be  the  differentiations  of  the  force  passing  through  them. 

It  follows  obviously  from  this,  that  if  structure  progresses 
from  the  homogeneous,  indefinite,  and  incoherent,  to  the 
heterogeneous,  definite,  and  coherent,  so  too  must  function. 
If  the  number  of  different  parts  in  an  aggregate  must  deter- 
mine the  number  of  differentiations  produced  in  the  forces 
passing  through  it — if  the  distinctness  of  these  parts  from  each 
other,  must  involve  distinctness  in  their  reactions,  and  there- 
fore distinctness  between  the  divisions  of  the  differentiated 
furce ;  there  cannot  but  be  a  complete  parallelism  between 
the  development  of  structure  and  the  development  of  func- 
tion. If  structure  advances  from  the  simple  and  general  to 
the  complex  and  special,  function  must  do  the  same. 


CHAPTER  IV. 

WASTE    AND    REPAIR. 

§  62.  Throughout  the  vegetal  kingdom,  the  processes  of 
SYaste  and  Repair  are  comparatively  insignificant  in  their 
amounts.  Though  plants,  and  especially  certain  parts  of 
thera,  do,  in  the  absence  of  light  or  under  particular  con- 
ditions, give  out  carbonic  acid ;  yet  this  carbonic  acid, 
assuming  it  to  indicate  consumption  of  tissue,  indicates  but  a 
small  consumption.  Of  course  if  there  is  little  waste,  there 
can  be  but  little  repair — that  is,  little  of  the  interstitial  repair 
which  restores  the  integrity  of  parts  worn  by  functional  acti- 
vity. Nor,  indeed,  is  there  displayed  by  plants  in  any  con- 
siderable degree,  if  at  all,  that  other  species  of  repair  which 
consists  in  the  restoration  of  lost  or  injured  organs.  Torn 
leaves  and  the  shoots  that  are  shortened  by  the  pruner,  do 
not  reproduce  their  missing  parts ;  and  though  when  the 
branch  of  a  tree  is  cut  off  close  to  the  trunk,  the  place  is  in 
the  course  of  years  covered  over,  it  is  not  by  any  reparative 
action  in  the  wounded  surface,  but  by  the  lateral  growth  of 
the  adjacent  bark.  Hence,  without  saying  that  Waste  and 
Repair  do  not  go  on  at  all  in  plants,  we  may  fitly  pass  them 
Dver  as  of  no  importance. 

There  are  but  slight  indications  of  waste  in  those  lower 

orders   of  animals  which,  by   their  comparative  inactivitv, 

Bhow  themselves  least  removed   from  vegetal  life.     Actinia 

k»pt  in  an  aquarium,  do  not  appreciably  diminish  in  bulk 

12 


170  THE    INDUCTIONS   OF    BIOLOGY. 

from  prolonged  abstinence.  Even  fish,  though,  much  more 
active  than  most  other  aquatic  creatures,  appear  to  undergo 
but  little  loss  of  substance  when  kept  unfed  during  con- 
siderable periods.  .Reptiles,  too,  maintaining  no  great 
temperature,  and  passing  their  lives  mostly  in  a  state  of 
torpor,  suffer  but  little  diminution  of  mass  by  waste.  When, 
however,  we  turn  to  those  higher  orders  of  animals  which 
are  active  and  hot-blooded,  we  see  that  waste  is  rapid : 
producing  when  unchecked,  a  notable  decrease  in  bulk 
and  weight,  ending  very  shortly  in  death.  Besides 

finding  that  waste  is  inconsiderable  in  creatures  that  pro- 
duce but  little  insensible  and  sensible  motion,  and  that  it 
becomes  conspicuous  in  creatures  that  produce  much  insen- 
sible and  sensible  motion  ;  we  find  that  in  the  same  crea- 
tures there  is  most  waste  when  most  motion  is  generated. 
This  is  clearly  proved  by  hybernating  animals.  "  Va- 
lentin found  that  the  waking  marmot  excreted  in  the  average 
75  times  more  carbonic  acid,  and  inhaled  41  times  more 
oxygen  than  the  same  animal  in  the  most  complete  state  of 
hybernation.  The  stages  between  waking  and  most  pro- 
found hybernation  yielded  intermediate  figures.  A  waking 
hedgehog  yielded  about  20" 5  times  more  carbonic  acid,  and 
consumed  18*4  times  more  oxygen  than  one  in  the  state  of  hy- 
bernation." If  we  take  these  quantities  of  absorbed  oxygen 
and  excreted  carbonic  acid,  as  indicating  something  like  the 
relative  amounts  of  consumed  organic  substance,  we  see 
that  there  is  a  striking  contrast  between  the  waste  ac- 
companying the  ordinary  state  of  activity,  and  the  waste 
accompanying  complete  quiescence  and  reduced  temperature. 
This  difference  is  still  more  definitely  shown  by  the  fact, 
that  the  mean  daily  loss  from  starvation  in  rabbits  and 
guinea-pigs,  bears  to  that  from  hybernation,  the  proportion 
of  183  :  1.  Among  men  and  domestic  animals,  the  relation 
between  degree  of  waste  and  amount  of  expended  force, 
though  one  respecting  which  there  is  little  doubt,  is  lesa 
distinctly  demonstrable ;  since  waste  is  not  allowed  to  go  on 


WASTE    AND    REPAIR.  171 

rtninterfered  with.  "We  have  however  in  the  lingering  lives  of 
invalids  who  are  able  to  take  scarcely  any  nutriment,  but 
are  kept  warm  and  still,  an  illustration  of  the  extent  to 
which  waste  diminishes  as  the  expenditure  of  force  declines. 

Besides  the  connexion  between  the  waste  of  the  organism 
as  a  whole,  and  the  production  of  sensible  and  insensible 
motion  by  the  organism  as  a  whole ;  there  is  a  traceable 
connexion  between  the  waste  of  special  parts  and  the  activi- 
ties of  such  special  parts.  Experiments  have  shown  that  "  the 
starving  pigeon  daily  consumes  in  the  average  40  times 
more  muscular  substance  than  the  marmot  in  the  state  of 
torpor,  and  only  11  times  more  fat,  33  times  more  of  the 
tissue  of  the  alimentary  canal,  183  times  more  liver,  15 
times  more  lung,  5  times  more  skin."  That  is  to  s&y,  in 
the  hybernating  animal  the  parts  least  consumed  are  the 
almost  totally  quiescent  motor-organs,  and  the  part  most 
consumed  is  the  hydro-carbonaceous  deposit  serving  as  a 
store  of  force  ;  whereas  in  the  pigeon,  similarly  unsupplied 
with  food  but  awake  and  active,  the  greatest  loss  takes  place 
in  the  motor-organs.  The  relation  between  special 

activity  and  special  waste,  is  illustrated  too  in  the  daily 
experiences  of  all :  not  indeed  in  the  measurable  decrease  of 
the  active  parts  in  bulk  or  weight,  for  this  we  have  no  means 
of  ascertaining ;  but  in  the  diminished  ability  of  such  parts 
to  perform  their  functions.  That  legs  exerted  for  many  hours 
in  walking,  and  arms  long  strained  in  rowing,  lose  their 
powers — that  eyes  become  enfeebled  by  reading  or  writing 
without  intermission — that  concentrated  attention  unbroken 
by  rest,  so  prostrates  the  brain  as  to  incapacitate  it  for  think- 
ing; are  familiar  truths.  And  though  we  have  no  direct 
evidence  to  this  effect,  there  is  little  danger  in  concluding  that 
muscles  exercised  until  they  ache  or  become  stiff,  and  nerves 
of  sense  rendered  weary  or  obtuse  by  work,  are  organs  so 
much  wasted  by  action  as  to  be  partially  incompetent. 

Repair  is  everywhere  and  alwa}^s  making  up  for  waste 
Though  the  two  processes  vary  in  their  relative  rates,  both 


172  THE    INDUCTIONS    OF    BIOLOGY 

are  constantly  going  on.  Though  during  the  active,  waking 
state  of  an  animal,  waste  is  in  excess  of  repair,  yet  repair  is 
in  progress  ;  and  though  during  sleep,  repair  is  in  excess  of 
waste,  yet  some  waste  is  necessitated  by  the  carrying  on  of 
certain  never-ceasing  functions.  The  organs  of  these  never- 
ceasing  functions  furnish,  indeed,  the  most  conclusive  proofs 
of  the  simultaneity  of  repair  and  waste.  Day  and  night  the 
heart  never  stops  beating,  but  only  varies  in  the  rapidity 
and  vigour  of  its  beats  ;  and  hence  the  loss  of  substance 
which  its  contractions  from  moment  to  moment  entail,  must 
from  moment  to  moment  be  made  good.  Day  and  night 
the  lungs  dilate  and  collapse  ;  and  the  muscles  which  make 
them  do  this,  must  therefore  be  ever  kept  in  a  state  of  integ- 
rity by  a  repair  which  keeps  pace  with  waste,  or  which 
alternately  falls  behind  and  gets  in  advance  of  it  to  a  very 
slight  extent. 

On  a  survey  of  the  facts,  we  see,  as  we  might  expect  to 
see,  that  repair  is  most  rapid  when  activity  is  most  reduced. 
Assuming  that  the  organs  which  absorb  and  circulate  nutri- 
ment are  in  proper  order,  the  restoration  of  the  organism 
to  a  state  of  integrity,  after  the  disintegration  consequent 
on  expenditure  of  force,  is  proportionate  to  the  diminution 
in  expenditure  of  force.  Thus  we  all  know  that  those 
who  are  in  health,  feel  the  greatest  return  of  vigour  after 
profound  sleep — after  complete  cessation  of  motion.  "We 
know  that  a  night  during  which  the  quiescence,  bodily 
and  mental,  has  been  less  decided,  is  usually  not  followed  by 
that  spontaneous  overflow  of  energy  that  indicates  a  high 
state  of  efficiency  throughout  the  organism.  "We  know, 
again,  that  long- continued  recumbency,  even  with  wakeful- 
ness (providing  the  wakefulness  is  not  the  result  of  disorder), 
h  followed  by  a  certain  renewal  of  strength ;  though  a  re- 
newal less  than  that  which  would  have  followed  the  greater 
inactivity  of  slumber.  We  know,  too,  that  when  exhausted 
by  labour,  sitting  brings  a  partial  return  of  vigour.  And 
we  also  know  that  after  the   violent  exertion   of  running 


WASTE    AND   RErAIR  173 

a  lapse  into  the  less  violent  exertion  of  walking,  results  in 
a  gradual  disappearance  of  that  prostration  which  the  run- 
ning produced.  This  series  of  illustrations  conclusively 
proves  that  the  rebuilding  of  the  organism  is  ever  making 
up  for  the  pulling  down  of  it  caused  by  action ;  and  that  the 
effect  of  this  rebuilding  becomes  manifest,  in  proportion  as 
the  pulling  down  is  less  rapid.  From  each  digested  meal, 
there  is  every  few  hours  absorbed  into  the  mass  of  prepared 
nutriment  circulating  through  the  body,  a  fresh  supply  of 
the  needful  organic  compounds ;  and  from  the  blood  thus 
occasionally  re-enriched,  the  organs  through  which  it  passes 
are  ever  taking  up  materials  to  replace  the  materials  used  up 
in  the  discharge  of  functions.  During  activity,  the  reinte- 
gration falls  in  arrear  of  the  disintegration ;  until,  as  a  conse- 
quence, there  presently  comes  a  general  state  of  functional 
languor  ;  ending,  at  length,  in  a  quiescence  which  permits  the 
reintegration  to  exceed  the  disintegration,  and  restore  the 
parts  to  their  state  of  integrity.  Here,  as  wherever  there 
are  antagonistic  actions,  we  see  rhythmical  divergences  on 
opposite  sides  of  the  medium  state — changes  which  equilibrate 
each  other  by  their  alternate  excesses.  (First  Principles, 
§§  96,  133.) 

Illustrations  are  not  wanting  of  special  repair,  that  is 
similarly  ever  in  progress,  and  similarly  has  intervals  during 
which  it  falls  below  waste  and  rises  above  it.  Every  one 
knows  that  a  muscle,  or  a  set  of  muscles,  continuously  strain- 
ed, as  by  holding  out  a  weignt  at  arm's  length,  soon  loses  its 
power ;  and  that  it  recovers  its  power  more  or  less  fully  after 
a  short  rest.  The  several  organs  of  special  sensation  yield 
us  like  experiences  :  strong  tastes,  powerful  odours,  and  loud 
sounds,  temporarily  unfit  the  nerves  impressed  by  them,  for 
appreciating  faint  tastes,  odours,  or  sounds  ;  but  these  inca- 
pacities are  remedied  by  brief  intervals  of  repose.  Vision 
still  better  illustrates  this  simultaneity  of  waste  and  repair 
Looking  at  the  sun  so  affects  the  eye  that,  for  a  short  time, 
it  cannot  perceive  the  ordinarv  contrasts  of  light  and  shade. 


174  THE    INDUCTIONS    OF    BIOLOGY. 

After  gazing  at  a  bright  light  of  a  particular  colour,  we  see 
on  turning  the  eyes  to  adjacent  objects,  an  image  of  the 
complementary  colour;  showing  that  the  retina  has,  for  the 
moment,  lost  the  power  to  feel  small  amounts  of  those  rays 
which  have  strongly  affected  it.  Such  inabilities  disappear 
in  a  few  seconds  or  a  few  minutes,  according  to  circumstances. 
And  here,  indeed,  we  are  introduced  to  a  conclusive  proof 
that  special  repair  is  ever  neutralizing  special  waste.  For 
the  rapidity  with  which  the  eyes  recover  their  sensitiveness, 
varies  with  the  reparative  power  of  the  individual.  In  youth, 
the  visual  apparatus  is  so  quickly  restored  to  its  state  of  in- 
tegrity, that  many  of  these  photogenes,  as  they  are  called, 
cannot  be  perceived.  When  sitting  on  the  far  side  of  a  room, 
and  gazing  out  of  the  window  against  a  light  sky,  a  person 
who  is  debilitated  by  disease  or  advancing  years,  perceives, 
on  transferring  the  gaze  to  the  adjacent  wall,  a  momentary 
negative  image  of  the  window — the  sash-bars  appearing  light 
and  the  squares  dark  ;  but  a  young  and  healthy  person  has 
no  such  experience.  With  a  rich  blood  and  vigorous  circu- 
lation, the  repair  of  the  visual  nerves  after  impressions  of 
moderate  intensity,  is  nearly  instantaneous. 

Function  carried  to  excess,  may  produce  waste  so  great, 
that  repair  cannot  make  up  for  it  during  the  ordinary 
daily  periods  of  rest ;  and  there  may  result  incapacities  of 
the  overtaxed  organs,  lasting  for  considerable  periods.  We 
know  that  eyes  strained  by  long-continued  minute  work,  lose 
their  power  for  months  or  years  :  perhaps  suffering  an  injury 
which  they  never  wholly  recover.  Brains,  too,  are  often  so 
unduly  worked  that  permanent  relaxation  fails  to  restore 
them  to  vigour.  Even  of  the  motor  organs  the  like  holds. 
The  most  frequent  cause  of  what  is  called  "  wasting  palsy,'*' 
or  atrophy  of  the  muscles,  is  habitual  excess  of  exertion :  the 
proof  being,  that  the  disease  occurs  most  frequently  among 
those  engaged  in  laborious  handicrafts,  and  usually  attacks 
first  the  muscles  that  have  been  most  worked. 

There  has  yet  to  be  noticed  another  kind  of  repair ; — that 


WASTE    AND    REPAIR.  175 

namely,  by  which  injured  or  lost  parts  are  restored.  Among 
the  Hydrozoa  it  is  common  for  any  portion  of  the  body  to  re- 
produce the  rest ;  even  though  the  rest  to  be  so  reproduced 
is  the  greater  part  of  the  whole.  In  the  more  highly-organ- 
ized Actinozoa,  the  half  of  an  individual  will  grow  into  a 
complete  individual.  Some  of  the  lower  Annelids,  as  the 
Nais,  may  be  cut  into  thirty  or  forty  pieces,  and  each  piece  will 
eventually  become  a  perfect  animal.  As  we  ascend  to  higher 
forms,  we  find  this  reparative  power  much  diminished,  though 
still  considerable.  The  reproduction  of  a  lost  claw  by  a 
lobster  or  crab,  is  a  familiar  instance.  Some  of  the  inferior 
Vertebrate  also,  as  lizards,  can  develop  new  limbs  or  new 
tails,  in  place  of  those  that  have  been  cut  off;  and  can  even 
do  this  several  times  over,  though  with  decreasing  complete- 
ness. The  highest  animals,  however,  thus  repair  themselves 
to  but  a  very  small  extent.  Mammals  and  birds  do  it  only 
in  the  healing  of  wounds ;  and  very  often  but  imperfectly 
even  in  this.  For  in  muscular  and  glandular  organs,  the 
tissues  destroyed  are  not  properly  reproduced,  but  are  re- 
placed by  tissue  of  an  irregular  kind,  which  serves  to  hold 
the  parts  together.  So  that  the  power  of  reproducing  lost  parts 
is  greatest  where  the  organization  is  lowest ;  and  almost  dis- 
appears where  the  organization  is  highest.  And  though  we 
cannot  say  that  between  these  extremes  there  is  a  constant  in- 
verse relation  between  reparative  power  and  degree  of  organ- 
ization; yet  we  may  say  that  there  is  some  approach  to 
euch  a  relation. 

§  63.  There  is  a  very  obvious  and  complete  harmony  be- 
tween the  first  of  the  above  inductions,  and  the  deduction 
that  follows  immediately  from  first  principles.  "We  have 
already  seen  (§  23)  "  that  whatever  amount  of  power  an 
organism  expends  in  any  shape,  is  the  correlate  and  equi- 
valent of  a  power  that  was  taken  into  it  from  without." 
Motion,  sensible  or  insensible,  generated  by  an  organism,  ia 
insensible  motion  which  was  absorbed  in  producing  certain 


176  THE    INDUCTIONS    OF    BIOLOGY. 

chemical  compounds  appropriated  by  the  organism  under 
the  form  of  food.  As  much  power  as  was  required  to  raise 
the  elements  of  these  complex  atoms  to  their  state  of  unsta- 
ble equilibrium,  is  given  out  in  their  falls  to  a  state  of  stable 
equilibrium ;  and  having  fallen  to  a  state  of  stable  equilib- 
rium, they  can  give  out  no  further  power,  but  have  to  be 
got  rid  of  as  inert  and  useless.  It  is  an  inevitable  corollary 
"  from  the  persistence  of  force,  that  each  portion  of  mechanical 
or  other  energy  which  an  organism  exerts,  implies  the  trans- 
formation of  as  much  organic  matter  as  contained  this 
energy  in  a  latent  state  ; "  and  that  this  organic  matter  in 
yielding  up  its  latent  energy,  loses  its  value  for  the  purposes 
of  life,  and  becomes  waste  matter  needing  to  be  excreted. 
The  loss  of  these  complex  unstable  substances  must  hence  be 
proportionate  to  the  quantity  of  expended  force.  Here  then 
is  the  rationale  of  certain  general  facts  lately  indicated. 
Plants  do  not  waste  to  any  considerable  degree,  for  the  obvi- 
ous reason  that  the  sensible  and  insensible  motions  they 
generate  are  inconsiderable.  Between  the  small  waste,  small 
activity,  and  low  temperature  of  the  inferior  animals,  the  rela- 
tion is  similarly  one  admitting  of  a  priori  establishment.  Con- 
versety,  the  rapid  waste  of  energetic,  hot-blooded  animals 
might  be  foreseen  with  equal  certainty.  And  not  less  mani- 
festly necessary  is  the  variation  in  waste  which,  in  the  same 
organism,  attends  the  variation  in  the  heat  and  mechanical 
motion  produced. 

Between  the  activity  of  a  special  part  and  the  waste  of 
that  part,  a  like  relation  may  be  deductively  inferred  ;  though, 
it  cannot  be  inferred  that  this  relation  is  equally  defi- 
nite. Were  the  activity  of  every  organ  quite  independent 
of  the  activities  of  other  organs,  we  might  expect  to  trace 
out  this  relation  distinctly  ;  but  since  one  part  of  the  force 
which  any  organ  expends,  is  derived  from  materials  brought 
to  it  by  the  blood  from  moment  to  moment  in  quantities 
varying  with  the  demand,  and  since  another  part  of  the 
force  which  suoh  organ  expends,  comes  to  it  in  the  shape  of 


WASTE    AND    REPAIR.  1 1  ( 

nervous  discharges  from  distant  organs  ;  it  is  clear  that  spe- 
cial waste  and  general  waste  are  too  much  entangled  to 
admit  of  a  definite  relation  being  established  between  special 
waste  and  special  activity.  We  may  fairly  say,  however, 
that  this  relation  is  quite  as  manifest  as  we  can  reasonably 
anticipate. 

§  64.  Deductive  interpretation  of  the  phenomena  of  He- 
pair,  is  by  no  means  so  easy.  The  tendency  displayed  by  an 
animal  organism,  as  well  as  by  each  of  its  organs,  to  return 
to  a  state  of  integrity  by  the  assimilation  of  new  matter, 
when  it  has  undergone  the  waste  consequent  on  activity,  is  a 
tendency  which  is  not  manifestly  deducible  from  first  princi- 
ples ;  though  it  appears  to  be  in  harmony  with  them.  If 
in  the  blood  there  existed  ready-formed  units  exactly  like  in 
kind  to  those  of  which  each  organ  consists,  the  sorting  of  these 
units,  ending  in  the  union  of  each  kind  with  already  existing 
groups  of  the  same  kind,  would  be  merely  a  good  example  of 
Differentiation  and  Integration  [First  Principles,  §  123).  It 
would  be  analogous  to  the  process  by  which,  from  a  mixed 
solution  of  salts,  there  are  deposited  segregated  masses  of 
these  salts,  in  the  shape  of  different  crystals.  But  as  already 
said  (§  54),  though  the  selective  assimilation  by  which  the 
repair  of  organs  is  effected,  no  doubt  results  in  part  from  an 
action  of  this  kind,  which  is  consequent  on  the  persistence  of 
force  (First  Principles,  §  129),  the  facts  cannot  be  thus  wholly 
accounted  for ;  since  organs  are  in  part  made  up  of  units 
that  do  not  exist  as  such  in  the  circulating  fluidu.  The  pro- 
cess becomes  comprehensible  however,  if  it  be  shown  that,  as 
suggested  in  §  54,  groups  of  compound  units  have  a  certain 
power  of  moulding  adjacent  fit  materials  into  units  of  their 
own  form.  Let  us  see  whether  there  is  not  reason  to  think 
such  a  power  exists. 

"  The  poison  of  small-pox  or  of  scarlatina,"  remarks  Mr. 
Paget,  "  being  once  added  to  the  blood,  presently  affects  the 
composition  of   the  whole :    the  disease  pursues  its  course, 


178  THE    INDUCTIONS    OF    BIOLOGY. 

and,  if  recovery  ensue,  the  blood  will  seem  to  have  returned 
to  its  previous  condition  :  yet  it  is  not  as  it  was  before  ;  for 
now  the  same  poison  may  be  added  to  it  with  impunity." 
*  *  *  "  The  change  once  effected,  may  be  maintained 
through  life.  And  herein  seems  to  be  a  proof  of  the  assimil- 
ative force  in  the  blood  ;  for  there  seems  no  other  mode  of 
explaining  these  cases  than  by  admitting  that  the  altered 
particles  have  the  power  of  assimilating  to  themselves  all 
those  by  which  they  are  being  replaced  :  in  other  words,  all 
the  blood  that  is  formed  after  such  a  disease  deviates  from 
the  natural  composition,  so  far  as  to  acquire  the  peculiarity 
engendered  by  the  disease :  it  is  formed  according  to  the 
altered  model."  Now  if  the  compound  molecules  of  the 
blood,  or  of  an  organism  considered  in  the  aggregate,  have 
the  power  of  moulding  into  their  own  type,  the  matters 
which  they  absorb  as  nutriment ;  and  if,  as  Mr  Paget 
points  out,  they  have  the  power  when  their  type  has  been 
changed  by  disease,  of  moulding  all  materials  afterwards 
received  into  the  modified  type ;  may  we  not  reasonably 
suspect  that  the  more  or  less  specialized  molecules  of  each 
organ,  have,  in  like  manner,  the  power  of  moulding  the 
materials  which  the  blood  brings  to  them,  into  similarly 
specialized  molecules  ?  The  one  conclusion  seems  to  be  a 
corollarv  from  the  other.  Such  a  power  cannot  be  claimed 
for  the  component  units  of  the  blood,  without  being  con- 
ceded to  the  component  units  of  every  tissue.  Indeed  the 
assertion  of  this  power  is  little  more  than  an  assertion  of  the 
fact,  that  organs  composed  of  specialized  units  are  capable 
of  resuming  their  structural  integrity,  after  they  have  been 
wasted  by  function.  For  if  they  do  this,  they  must  do  it  by 
forming  from  the  materials  brought  to  them,  certain  special- 
ized units  like  in  kind  to  those  of  which  they  are  composed , 
and  to  say  that  they  do  this,  is  to  say  that  their  component 
units  have  the  power  of  moulding  fit  materials  into  othei 
units  of  the  same  order. 

The  repair  of  a  wasted  tissue  may  therefore  be  considered 


WASTE    AND   REPAIR.  179 

as  duo  to  forces  analogous  to  those  by  which  a  crystal  repro* 
duces  its  lost  apex,  when  placed  in  a  solution  like  that  from 
which  it  was  formed.  In  either  case,  a  mass  of  units  of  a 
given  kind,  shows  a  power  of  integrating  with  itself  diffused 
units  of  the  same  kind  :  the  only  difference  being,  that  the 
organic  mass  of  units  arranges  the  diffused  units  into  special 
compound  forms,  before  integrating  them  with  itself.  In 
the  case  of  the  crystal,  this  reintegration  is  ascribed  to 
polarity — a  power  of  whose  nature  we  know  nothing.  What- 
ever be  its  nature,  however,  it  appears  probable  that  the 
power  by  which  organs  repair  themselves  from  the  nutritive 
matters  circulating  through  them,  is  of  the  same  order. 

§  65.  That  other  kind  of  repair  which  shows  itself  in  the 
regeneration  of  lost  members,  is  comprehensible  only  as  an 
effect  of  actions  like  those  just  referred  to.  The  ability  of 
an  organism  to  recompletc  itself  when  one  of  its  parts  has 
been  cut  off,  is  of  the  same  order  as  the  ability  of  an  injured 
crystal  to  recomplete  itself.  In  either  case,  the  newty-assimi- 
lated  matter  is  so  deposited  as  to  restore  the  original  outline. 
And  if  in  the  case  of  the  crystal,  we  say  that  the  whole 
aggregate  exerts  over  its  parts,  a  force  which  constrains  the 
newly-integrated  atoms  to  take  a  certain  definite  form  ;  we 
must  in  the  case  of  the  organism,  assume  an  analogous  force. 
This  is,  in  truth,  not  an  hypothesis  :  it  is  nothing  more  than 
a  generalized  expression  of  the  facts.  If  when  the  leg  of  a 
lizard  has  been  amputated,  there  presently  buds  out  the  germ 
of  a  new  one,  which,  passing  through  phases  of  development 
like  those  of  the  original  leg,  eventually  assumes  a  like  shape 
and  structure  ;  we  assert  nothing  more  than  what  we  see, 
when  we  assert  that  the  organism  as  a  whole  exercises  such 
power  over  the  newly- forming  limb,  as  makes  it  a  repetition 
of  its  predecessor,  if  a  leg  is  reproduced  where  there  was  a 
leg,  and  a  tail  where  there  was  a  tail ;  we  have  no  alternative 
but  to  conclude  that  the  aggregate  forces  of  the  body,  con- 
trol the  formative  processes  going  on  in  each  part.     And  on 


ISO  THE    INDUCTIONS    OF    BIOLOGY. 

contemplating  these  facts  in  connexion  with  various  kindred 
ones,  there  is  suggested  the  hypothesis,  that  the  form  of  each 
species  of  organism  is  determined  by  a  peculiarity  in  the  con- 
stitution of  its  units — that  these  have  a  special  structure  in 
which  they  tend  to  arrange  themselves ;  just  as  have  the 
simpler  units  of  inorganic  matter.  Let  us  glance  at  the  evi- 
dences which  more  especially  thrust  this  conclusion  upon  us. 

A  fragment  of  a  Begonia-leaf,  imbedded  in  fit  soil  and  kept 
at  an  appropriate  temperature,  will  develop  a  young  Bego- 
nia ;  aud  so  small  is  the  fragment  which  is  thus  capable  of 
originating  a  complete  plant,  that  something  like  a  hundred 
plants  might  be  produced  from  a  single  leaf.  The  friend  to 
whom  I  owe  this  observation,  tells  me  that  various  succulent 
plants  have  like  powers  of  multiplication.  Illustrating  a 
similar  power  among  animals, we  have  the  often-cited  exper- 
iments of  Trembley  on  the  common  polype.  Each  of  the 
four  pieces  into  which  one  of  these  creatures  was  cut,  grew 
into  a  perfect  individual.  In  each  of  these  again,  bisection 
and  tri-section  effected  a  like  result.  And  so  with  their 
segments,  similarly  produced,  until  as  man}'-  as  fifty  polypes 
had  resulted  from  the  original  one.  Bodies  when  cut  off 
regenerated  heads  ;  heads  regenerated  bodies  ;  and  when  a 
polype  had  been  divided  into  as  many  pieces  as  was  practica- 
ble, nearly  every  piece  survived  and  became  a  complete 
animal.  What,    now,   is   the    implication  ?    We 

cannot  say  that  in  each  portion  of  a  Begonia-leaf,  and  in 
every  fragment  of  a  Hydra's  body,  there  exists  a  ready- 
formed  model  of  the  entire  organism.  Even  were  there 
warrant  for  the  now  abandoned  doctrine,  that  the  germ  of 
every  organism  contains  the  perfect  organism  in  miniature,  it 
still  could  not  be  contended  that  each  considerable  part  of  the 
perfect  organism  resulting  from  such  a  germ,  contains  another 
such  miniature.  Indeed  the  one  hypothesis  obviously  nega- 
tives the  other.  We  have  therefore  no  alternative  but  to 
say,  that  the  living  particles  composing  one  of  these  frag- 
ments, have  an  innate  tendency  to  arrange  themselves  into 


WASTE    AND    REPAIR.  181 

the  shape  of  the  organism  to  which  they  belong.  We  must 
infer  that  a  plant  or  animal  of  any  species,  is  made  np  of 
special  units,  in  all  of  which  there  dwells  the  intrinsic  apti- 
tude to  aggregate  into  the  form  of  that  species  :  jast  as  in  the 
atoms  of  a  salt,  there  dwells  the  intrinsic  aptitude  to  crystal- 
lize in  a  particular  way.  It  seems  difficult  to  conceive  that 
this  can  be  so ;  but  we  see  that  it  is  so.  Groups  of  units 
taken  from  an  organism  (providing  they  are  of  a  certain 
bulk  and  not  much  differentiated  into  special  structures)  have 
this  power  of  re-arranging  themselves;  and  we  are  thus 
compelled  to  recognize  the  tendency  to  assume  the  specific 
form,  as  inherent  in  all  parts  of  the  organism.  Mani- 

festly too,  if  we  are  thus  to  interpret  the  reproduction 
of  an  organism  from  one  of  its  amorphous  fragments, 
we  must  thus  interpret  the  reproduction  of  any  minor 
portion  of  an  organism  by  the  remainder.  When  in  place 
of  its  lost  claw,  a  lobster  puts  forth  from  the  same  spot  a 
cellular  mass,  which,  while  increasing  in  bulk,  assumes  the 
form  and  structure  of  the  original  claw ;  we  can  have  no 
hesitation  in  ascribing  this  result  to  a  play  of  forces  like 
that  which  moulds  the  materials  contained  in  a  piece  of 
Begonia-leaf  into  the  shape  of  a  young  Begonia.  In  the  one 
case  as  in  the  other,  the  vitalized  molecules  composing  the 
tissues,  show  their  proclivity  towards  a  particular  arrange- 
ment ;  and  whether  such  proclivity  is  exhibited  in  repro- 
ducing the  entire  form,  or  in  completing  it  when  rendered 
imperfect,  matters  not. 

For  this  property  there  is  no  fit  term.  If  we  accept  the 
word  polarity,  as  a  name  for  the  force  by  which  inorganic 
units  are  aggregated  into  a  form  peculiar  to  them ;  we  may 
apply  this  word  to  the  analogous  force  displayed  by  organic 
units.  But,  as  above  admitted,  polarity,  as  ascribed  to  atoms, 
is  but  a  name  for  something  of  which  we  are  ignorant— a 
name  for  a  hypothetical  property  which  as  much  needs  ex- 
planation as  that  which  it  is  used  to  explain.  Nevertheless, 
in  default  of  another  word,  we  must  employ  this  :    taking 


182  THE    INDUCTIONS    OF    BIOLOGY. 

care,  however,  to  restrict  its  meaning.  If  we  simply  substi- 
tute the  term  polarity,  for  the  circuitous  expression — the 
power  which  certain  units  have  of  arranging  themselves 
into  a  special  form,  we  may,  without  assuming  anything 
more  than  is  proved,  use  the  term  organic  polarity  or  po- 
larity of  the  organic  units,  to  signify  the  proximate  cause 
of  the  ability  which  organisms  display  of  reproducing  lost 
parts. 

§  66.  As  we  shall  have  frequent  occasion  hereafter  to  refer 
to  these  units,  which  possess  the  property  of  arranging 
themselves  into  the  special  structures  of  the  organisms 
to  which  they  belong  ;  it  will  be  well  here  to  ask  what 
these  units  are,  and  by  what  name  they  may  be  most  fitly 
called. 

On  the  one  hand,  it  cannot  be  in  those  proximate  chemical 
compounds  composing  organic  bodies,  that  this  specific  polar- 
ity dwells.  It  cannot  be  that  the  atoms  of  albumen,  or  fibrine, 
or  gelatine,  or  the  hypothetical  protein- substance,  possess 
this  power  of  aggregating  into  specific  shapes ;  for  in 
such  case,  there  would  be  nothing  to  account  for  the  unlike- 
nesses  of  different  organisms.  Millions  of  species  of  plants 
and  animals,  more  or  less  contrasted  in  their  structures, 
are  all  mainly  built  up  of  these  complex  atoms.  But  if  the 
polarities  of  these  atoms  determined  the  forms  of  the  or- 
ganisms they  composed,  the  occurrence  of  such  endlessly 
varied  forms  would  be  inexplicable.  Hence,  what  we  may 
call  the  chemical  units,  are  clearly  not  the  possessors  of  this 
property. 

On  the  other  hand,  this  property  cannot  reside  in  what 
may  be  roughly  distinguished  as  the  morphological  units.  The 
germ  of  every  organism  is  a  microscopic  cell.  It  is  by 
multiplication  of  cells  that  all  the  early  developmental  changes 
are  effected.  The  various  tissues  which  successively  arise 
in  the  unfolding  organism,  are  primarily  cellular  ;  and  in 
many  of  them  the  formation  of  cells  continues  to  be,  through- 


WASTE    AND    REPAIR.  1£3 

out  life,  the  process  by  which  repair  is  carried  on.  But 
though  cells  are  so  generally  the  ultimate  visible  components 
of  organisms,  that  they  may  with  some  show  of  reason  be 
called  the  morphological  units  ;  yet,  as  they  are  not  uni- 
versal, we  cannot  say  that  this  tendency  to  aggregate  into 
specified  forms  dwells  in  them.  Finding  that  in  many 
cases  a  fibrous  tissue  arises  out  of  a  structureless  blastema, 
without  cell- formation  ;  and  finding  that  there  are  creatures, 
such  as  Rhizopods,  which  are  not  cellular,  but  nevertheless 
exhibit  vital  activities,  and  perpetuate  in  their  progeny 
certain  specific  distinctions ;  we  are  forbidden  to  ascribe  to 
cells  this  peculiar  power  of  arrangement.  Nor,  indeed, 
were  cells  universal,  would  such  an  hypothesis  be  acceptable  ; 
since  the  formation  of  a  cell  is,  to  some  extent  a  manifesta- 
tion of  this  same  peculiar  power. 

If,  then,  this  organic  polarity  can  be  possessed  neither  bj 
the  chemical  units  nor  the  morphological  units,  we  must 
conceive  it  as  possessed  by  certain  intermediate  units,  which 
we  may  term  physiological.  There  seems  no  alternative  but 
to  suppose,  that  the  chemical  units  combine  into  units 
immensely  more  complex  than  themselves,  complex  as  they 
are  ;  and  that  in  each  organism,  the  physiological  units 
produced  by  this  further  compounding  of  highly  compound 
atoms,  have  a  more  or  less  distinctive  character.  AVe  must 
conclude  that  in  each  case,  some  slight  difference  of  com- 
position in  these  units,  leading  to  some  slight  difference  in 
their  mutual  play  of  forces,  produces  a  difference  in  the  form 
which  the  aggregate  of  them  assumes. 

The  facts  contained  in  this  chapter,  form  but  a  small  part 
of  the  evidence  which  thrusts  this  assumption  upon  us.  We 
shall  hereafter  find  various  reasons  for  inferring  that  such 
physiological  units  exist,  and  that  to  their  specific  properties, 
more  or  less  unlike  in  each  plant  and  animal,  various  organio 
phenomena  are  due. 


CHAPTER  V. 
ADAPTATION. 

§  67.  In  plants,  waste  and  repair  being  scarcely  appre 
ciable,  there  are  not  likely  to  arise  appreciable  changes  in  the 
proportions  of  already- formed  parts.  The  only  divergences 
from  the  average  structure  of  a  species,  which  we  may  expect 
particular  conditions  to  produce,  are  those  producible  by  the 
action  of  these  conditions  on  parts  in  course  of  formation  ; 
and  such  divergences  we  do  find.  We  know  that  a  tree 
which,  standing  alone  in  an  exposed  position,  has  a  short 
and  thick  stem,  has  a  tall  and  slender  stem  when  it  grows 
in  a  wood ;  and  that  its  branches  then  take  a  different  inclin- 
ation. AVe  know  that  potato-sprouts  which,  on  reaching 
the  light,  develop  into  foliage,  will,  in  the  absence  of 
light,  grow  to  a  length  of  several  feet  without  foliage. 
And  every  in-door  plant  furnishes  proof,  that  shoots  and 
leaves,  by  habitually  turning  themselves  to  the  light,  exhibit 
a  certain  adaptation — an  adaptation  due,  as  we  must  suppose, 
to  the  special  effects  of  the  special  conditions  on  the  still  grow- 
ing parts.  In  animals,  however,  besides  analogous 
structural  changes  wrought  during  the  period  of  growth, 
by  subjection  to  circumstances  unlike  the  ordinary  circum- 
stances ;  there  are  structural  changes  similarly  wrought, 
after  maturity  has  been  reached.  Organs  that  have 
arrived  at  their  full  size,  possess  a  certain  modifiability ; 
bo    that    whiln    the    organism    as   a    whole,    retains    pretty 


ADAPTATION.  185 

nearly  the  same  bulk,  the  proportions  of  its  parts  may  bo 
considerably  varied.  Their  variations,  here  treated  of  under 
the  title  Adaptation,  depend  on  specialities  of  individual 
action.  We  saw  in  the  last  chapter,  that  the  actions  of  or- 
ganisms entail  re-actions  on  them ;  and  that  specialities  of 
action  entail  specialities  of  re-action.  Here  it  remains  to  be 
pointed  out,  that  the  special  actions  and  re-actions  do  not  end 
with  temporary  changes,  but  work  permanent  changes. 

If,  in  an  adult  animal,  the  waste  and  repair  in  all  parts 
were  exactly  balanced — if  each  organ  daily  gained  by 
nutrition,  exactly  as  much  as  it  lost  daily  by  the  discharge  of 
its  function — if  excess  of  function  were  followed  only  by  sucn 
excess  of  nutrition  as  balanced  the  extra  waste ;  it  is  clear 
that  there  would  occur  no  change  in  the  relative  sizes  of 
organs.  But  there  is  no  such  exact  balance.  If  the  excess 
of  function,  and  consequent  excess  of  waste,  is  moderate,  it  is 
not  simply  compensated  by  repair,  but  more  than  compensated 
— there  is  a  certain  increase  of  bulk.  This  is  true  to  some 
degree  of  the  organism  as  a  whole,  when  the  organism  is 
framed  for  activity.  A  considerable  waste  giving  considerable 
power  of  assimilation,  is  more  favourable  to  accumulation  of 
tissue,  than  is  quiescence  with  its  conrparatively  feeble  assimi- 
lation :  whence  results  a  certain  adaptation  of  the  whole 
organism  to  its  requirements.  But  it  is  more  especially  true 
of  the  parts  of  an  organism  in  relation  to  each  other.  The 
illustrations  fall  into  several  groups.  The  growth 

of  muscles  exercised  to  an  unusual  degree,  is  a  matter  of  com- 
mon observation.  In  the  often-cited  blacksmith's  arm,  the 
dancer's  legs,  and  the  jockey's  crural  adductors,  we  have 
marked  examples  of  a  modifiability  which  almost  every  one 
has  to  some  extent  experienced.  It  is  needless  to  multi- 
ply proofs.  The  occurrence  of  changes  in  the  struc- 
ture of  the  skin,  where  the  skin  is  exposed  to  a  stress  of 
function,  is  also  familiar.  That  thickening  of  the  epidermis 
on  a  labourer's  palm,  results  from  continual  pressure  and 
friction,  is  certain  :  those  who  have  not  before  exerted  theii 
13 


18()  TIfE    INDUCTIONS    OF    BIOLOGY. 

hands,  find  that  su<fh  an  exercise  as  rowing,  soon  begins  to 
produce  a  like  thickening.  This  relation  of  cause  and  effect 
is  still  better  shown  by  the  marked  indurations  at  the  ends  of 
a  violinist's  fingers.  Even  in  mucous  membrane,  which 
ordinarily  is  not  subject  to  mechanical  forces  of  any  intensity, 
similar  modifications  are  possible  :  witness  the  callosity  of 
the  gums  which  arises  in  those  who  have  lost  their  teeth,  and 
have   to   masticate   without   teeth.  The   vascular"! 

system  furnishes  good  instances  of  the  increased  growth  J 
that  follows  increased  function-  When,  because  of  some  | 
permanent  obstruction  to  the  circulation,  the.  heart  has  to 
exert  a  greater  contractile  force  on  the  mass  of  blood  which  it 
propels  at  each  pulsation  into  the  arteries,  and  when  there  re- 
sults the  laboured  action  known  as  palpitation  ;  there  usually 
occurs  dilatation,  or  hypertrophy,  or  a  mixture  of  the  two  : 
the  dilatation,  which  is  a  yielding  of  the  heart's  structure 
under  the  increased  strain,  implying  a  failure  to  meet  the 
emergency  ;  but  the  hypertrophy,  which  consists  in  a  thick- 
ening of  the  heart's  muscular  walls,  being  an  adaptation  of  it 
to  the  additional  effort  required.  Again,  when  an  aneurism 
in  some  considerable  artery  has  been  obliterated,  either  arti- 
ficially or  by  a  natural  inflammatory  process  ;  and  when  this 
artery  has  consequently  ceased  to  be  a  channel  for  the  blood ; 
some  of  the  adjacent  arteries  which  anastomose  with  it, 
become  enlarged,  so  as  to  carry  the  needful  quantity  of  blood 
to  the  parts  supplied.  Though  we  have  no  direct 

proof  of  analogous  modifications  in  nervous  structures ;  yet 
indirect  proof  is  given  by  the  greater  efficiency  that  fol- 
lows greater  activity.  This  is  manifested  alike  in  the 
senses  and  the  intellect.  The  palate  may  be  cultivated  in- 
to extreme  sensitiveness,  as  in  professional  tea-tasters.  An 
orchestral  conductor  gains  by  continual  practice,  an  unusually 
great  ability  to  discriminate  differences  of  sound.  And  in 
the  finger-reading  0f  the  blind,  we  have  evidence  that  the 
I  sense  of  touch  may  be  brought  by  exercise  to  a  far  higher 
capability  than  is  ordinaiy.     The  increase  of  power  which 


ADAPTATION.  187 

habitual  exertion  gives  to  mental  faculties,  needs  no  illustra- 
tion :  every  person  of  ed  ucation  has  personal  experience 
of  it.  Even  from  the  osseous  structures,  evidence 

may  be  drawn.  The  bones  of  men  accustomed  to  great  mus- 
cular action,  are  more  massive  and  have  more  strongly 
marked  processes  for  the  attachment  of  muscles,  than  the 
bones  of  men  who  lead  sedentary  lives  ;  and  a  like  contrast 
holds  between  the  bones  of  wild  and  tame  animals  of  the 
same  species.  Adaptations  of  another  order,  in  which  there 
is  a  qualitative  rather  than  a  quantitative  modification,  arise 
after  certain  accidents  to  which  the  skeleton  is  liable.  When 
the  hip-joint  has  been  dislocated,  and  long  delay  has  made  it 
impossible  to  restore  the  parts  to  their  proper  places,  the 
head  of  the  thigh-bone,  imbedded  in  the  surrounding  muscles, 
becomes  fixed  in  its  new  position  by  attachments  of  fibrous 
tissue,  which  afford  support  enough  to  permit  a  halting  walk. 
But  the  most  remarkable  modification  of  this  order  occurs  in 
ununited  fractures.  "False  joints "  are  often  formed — ■ 
joints  which  rudely  simulate  the  hinge  structure  or  the  ball- 
and-socket  structure,  according  as  the  muscles  tend  to  pro- 
duce a  motion  of  flexion  and  extension  or  a  motion  of  rota- 
tion. In  the  one  case,  according  to  Rokitansky,  the  two  ends 
of  the  broken  bone  become  smooth  and  covered  with  perios- 
teum and  fibrous  tissue,  and  are  attached  by  ligaments  that 
allow  a  certain  backward  and  forward  motion;  and  in  the 
other  case,  the  ends,  similarly  clothed  with  the  appropriate 
membranes,  become  the  one  convex  and  the  other  concave, 
are  inclosed  in  a  capsule,  and  are  even  occasionally  supplied 
with  synovial  fluid  ! 

The  general  truth  that  extra  function  is  followed  by  extra 
growth,  must  be  supplemented__by_the  equally  general  truth, 
that  bej^jidLaUimitJ_u^anyi^Qon  reached,  very  little,  if  any, 
further  modification  can  be  produced.  The  experiences  from 
which  we  draw  the~~one  inductionTlhrust  the  other  upon  us. 
After  a  time,  no  training  makes  the  pugilist  or  the  athlete 
any  stronger.     The  adult  gymnast  at  last  acquires  the  powci 


L88  THE    INDUCTIONS    OF    BIOLOGY. 

to  perform  certain  difficult  feats  •  but  certain  more  difficult 
feats,  no  additional  practice  enables  him  to  perform.  Years  of 
discipline  give  the  singer  a  pa1  'cular  loudness  and  range  of 
voice,  beyond  which  further  discipline  does  not  give  greater 
loudness  or  wider  range  :  on  the  contrary,  increased  vocal  ex- 
ercise, causing  a  waste  in  excess  of  repair,  is  often  followed 
by  decrease  of  power.  In   the  perceptions  we  sec 

similar  limits.  The  culture  which  exalts  the  susceptibility  of 
the  ear  to  the  intervals  and  harmonies  of  notes,  will  not 
turn  a  bad  ear  into  a  good  one.  Life-long  effort  fails  to 
make  this  artist  a  correct  draftsman,  or  that  a  fine  colourist : 
each  does  better  than  he  did  at  first,  but  each  fulls  short  of 
the  power  attained  by  some  other  artists.  Nor  is 

this  truth  less  clearly  illustrated  among  the  more  complex 
mental  powers.  Each  man  has  a  mathematical  faculty,  a 
poetical  faculty,  or  an  oratorical  faculty,  which  special  educa- 
tion improves  to  a  certain  extent.  But  unless  he  is.  unusually 
endowed  in  one  of  these  directions,  no  amount  of  education 
will  make  him  a  first-rate  mathematician,  a  first-rate  poet,  or 
a  first-rate  orator.  Thus  the  general  fact  appears  to 

be,  that  Avhile  in  each  individual,  certain  changes  in  the 
proportions  of  parts,  may  be  caused  by  variations  of  function, 
the  congenital  structure  of  each  individual  puts  a  limit  to 
the  modifiability  of  every  part.  Nor  is  this  true  of 

individuals  only  :  it  holds,  in  a  sense,  of  species.  Leaving 
open  the  question  whether,  in  indefinite  time,  indefinite  modi- 
fication may  not  be  produced  ;  experience  proves  that  within 
assigned  times,  the  changes  wrought  in  races  of  organisms 
by  changes  of  conditions  fall  within  narrow  limits.  We  see, 
for  instance,  that  though  by  discipline,  aided  by  selective 
breeding,  one  variety  of  horse  has  had  its  locomotive  power 
increased  considerably  beyond  the  locomotive  powers  of  other 
varieties  ;  yet  that  further  increase  takes  place,  if  at  all,  at  an 
inappreciable  rate.  The  different  kinds  of  dogs,  too,  in 
which  different  forms  and  capacities  have  been  established, 
lo  not  show  aptitudes  for  diverging  in  the  same  directions  «i1 


ADAPTATION. 


189 


considerable  rates.  In  domestic  animals  generally,  certain 
accessions  of  intelligence  have  been  produced  by  culture  ;  but 
accessions  beyond  these  are  inconspicuous.  It  seems  that 
in  each  species  of  organism,  there  is  a  margin  for  functional 
oscillations  on  all  sides  of  a  mean  state,  and  a  consequent 
margin  of  structural  variations  ;  that  it  is  possible  rapidly  to 
push  functional  and  structural  changes  towards  the  extreme 
of  this  margin  in  any  direction,  both  in  an  individual  and 
in  a  race  ;  but  that  to  push  these  changes  further  in  any 
direction,  and  so  to  alter  the  organism  as  to  bring  its  mean 
state  up  to  the  extreme  of  the  margin  in  that  direction,  is  a 
comparatively  slow  process.* 

We  have  also  to  note  that  the  limited  increase  of  size  pro- 
duced in  any  organ  by  a  limited  increase  of  its  function,  is 
not  maintained  unless  the  increase  of  function  is  permanent. 
A  mature  man  or  other  animal,  led  by  circumstances  into 
exerting  particular  members  in  unusual  degrees,  and  acquir- 
ing extra  size  and  power  in  these  members,  begins  to  lose 
such  extra  size  and  power  on  ceasing  to  exert  these  members; 
and  eventually  lapses  more  or  less  nearly  into  the  original 
state.  Legs  strengthened  by  a  pedestrian  tour,  become  weak 
again  after  a  prolonged  return  to  sedentary  life.  The 
acquired  ability  to  perform  feats  of  skill,  disappears  in  course 
of  time,  if  the  performance  of  them  is  given  up.  For  compara- 
tive failure  in  executing  a  piece  of  music,  in  playing  a  game 
at  chess,  or  in  anything  requiring  special  culture,  the  being 
out  of  practice  is  a  reason  of  which  every  one  recognizes  the 
validity.  It  is  observable,  too,  that  the  rapidity  and  com- 
pleteness with  which  an  artificial  power  is  lost,  is  proportionate 
to  the  shortness  of  the  cultivation  which  evoked  it.  One  who 
has  for  many  years  persevered  in  habits  which  exercise 
special  muscles  or  special  faculties  of  mind,  retains  the  extra 

*  Here,  as  in  sundry  places  throughout  this  chapter,  the  necessities  of  the  argu- 
ment have  obliged  me  to  forestall  myself,  by  assuming  the  conclusion  reached  in  a 
subsequent  chapter,  that  modifications  of  structure  produced  by  modifications  of 
function,  are  transmitted  to  offspring. 


190  THE    INDUCTIONS    OF    BIOLOGY. 

capacity  produced,  to  a  very  considerable  degree,  even  after  a 
long  period  of  desistance  ;  but  one  who  has  persevered  in  such 
habits  for  but  a  short  time,  has,  at  the  end  of  a  like  period, 
scarcely  any  of  the  facility  he  had  gained.  Here, 

too,  as  before,  successions  of  organisms  present  an  analogous 
fact.  A  species  in  which  domestication,  continued  through 
many  generations,  has  organized  certain  peculiarities ;  and 
which  afterwards,  escaping  domestic  discipline,  returns  to 
something  like  its  original  habits  ;  soon  loses,  in  great  mea- 
sure, such  peculiarities.  Though  it  is  not  true,  as  alleged, 
that  it  resumes  completely  the  ctructure  it  had  before  domes- 
tication ;  yet  it  approximates  to  that  structure.  The  Dingo, 
or  wild  dog  of  Australia,  is  one  of  the  instances  given 
of  this ;  and  the  wild  horse  of  South  America  is  another. 
Mankind,  too,  supplies  us  with  instances.  In  the  Austra- 
lian bush,  and  in  the  backwoods  of  America,  the  Anglo- 
Saxon  race,  in  which  civilization  has  developed  the  higher 
feelings  to  a  considerable  degree,  rapidly  lapses  into  compara- 
tive barbarism  :  adopting  the  moral  code,  and  sometimes  the 
habits,  of  savages. 

§  68.  It  is  important  to  reach,  if  possible,  some  rationale 
of  these  general  truths — especially  of  the  last  two.  A  right 
understanding  of  these  laws  of  organic  modification,  underlies 
a  right  understanding  of  the  great  question  of  species. 
While,  as  before  hinted  (§  40),  the  action  of  structure  on 
function,  is  one  of  the  factors  in  that  process  of  differentiation 
by  which  unlike  forms  of  plants  and  animals  are  produced, 
the  re-action  of  function  on  structure,  is  another  factor. 
Hence,  it  is  well  worth  while  inquiring  how  far  these  induc- 
tions are  deductively  interpretable. 

The  first  of  them  is  the  most  difficult  to  deal  with.  Why 
an  organ  exerted  somewhat  beyond  its  wont,  should  presently 
grow,  and  thus  meet  increase  of  demand  by  increase  of  sup- 
ply, is  not  obvious.  We  know,  indeed,  (First  Principles, 
§§  96,  133,)  that  of  necessity,  the  rhythmical  changes  pro- 


ADAPTATION.  191 

duced  by  antagonist  organic  actions,  cannot  any  of  them  bo 
carried  to  an  excess  in  one  direction,  without  there  being 
produced  an  equivalent  excess  in  the  opposite  direction.  It 
is  a  corollary  from  the  persistence  of  force,  that  any  deviation 
effected  by  a  disturbing  cause,  acting  on  some  member  of  a 
moving  equilibrium,  must  (unless  it  altogether  destroys  the 
moving  equilibrium)  be  eventually  followed  by  a  compensating 
deviation.  Hence,  that  excess  of  repair  should  succeed  ex- 
cess of  waste,  is  to  be  expected.  But  how  happens  the  mean 
state  of  the  organ  to  be  changed  ?  If  daily  extra  waste 
naturally  brings  about  daily  extra  repair,  only  to  an  equiva- 
lent extent,  the  mean  state  of  the  organ  should  remain  con- 
stant. How  then  comes  the  organ  to  augment  in  size  and 
power  ? 

Such  answer  to  this  question  as  we  may  hope  to  find,  must 
be  looked  for  in  the  effects  wrought  on  the  organism  as  a 
whole,  by  increased  function  in  one  of  its  parts.  For  since 
the  discharge  of  its  function  by  any  part,  is  possible  only  on 
condition  that  those  various  other  functions  on  which  its  own 
is  immediately  dependent,  are  also  discharged ;  it  follows 
that  excess  in  its  function  presupposes  some  excess  in  their 
functions.  Additional  work  given  to  a  muscle,  implies  ad- 
ditional work  given  to  the  branch  arteries  which  bring  it 
blood,  and  additional  work,  smaller  in  proportion,  to  the 
arteries  from  which  these  branch  arteries  come.  Similarly, 
the  smaller  and  larger  veins  which  take  away  the  blood,  as 
well  as  the  absorbents  which  carry  off  effete  products,  must 
have  more  to  do.  And  yet  further,  on  the  nervous  centres 
which  excite  the  muscle,  a  certain  extra  duty  must  fall.  But 
excess  of  waste  will  entail  excess  of  repair,  in  these  parts  as 
well  as  in  the  muscle.  The  several  appliances  by  which  the 
nutrition  and  excitation  of  an  organ  are  carried  on,  must  ulso 
be  influenced  by  this  rhythm  of  action  and  re-action  ;  and 
therefore,  after  losing  more  than  usual  by  the  destructive 
process,  they  must  gain  more  than  usual  by  the  constructive 
process.     But  temporarily-increased   efficiency  in   these  ap- 


192  THE    INDUCTIONS   OF    BIOLOGY. 

pliances  by  which  blood  and  nervous  force  are  brought  to  an 
organ,  will  cause  extra  assimilation  in  the  organ,  beyond 
that  required  to  balance  its  extra  expenditure.  Regarding 
the  functions  as  constituting  a  moving  equilibrium,  we  may 
say,  that  divergence  of  any  function  in  the  direction  of  in- 
crease, causes  the  functions  with  which  it  is  bound  up  to 
diverge  in  the  same  direction  ;  that  these  again  cause  the 
functions  which  they  are  bound  up  with,  also  to  diverge  in 
the  same  direction ;  and  that  these  divergences  of  the  con- 
nected functions,  allow  the  specially-affected  function  to  be 
carried  further  in  this  direction  than  it  could  otherwise  be 
— further  than  the  perturbing  force  could  carry  it  if  it  had  a 
fixed  basis. 

It  must  be  admitted  that  this  is  but  a  vague  explanation. 
Among  actions  so  involved  as  these,  we  can  scarcely  expect 
to  do  more  than  dimly  discern  a  harmony  with  first  princi- 
ples. That  the  facts  are  to  be  interpreted  in  some  such  way, 
may,  however,  be  inferred  from  the  circumstance  that  an 
extra  supply  of  blood  continues  for  some  time  to  be  sent  to 
an  organ  that  has  been  unusually  exercised  ;  and  that  when 
unusual  exercise  is  long  continued,  a  permanent  increase  of 
vascularity  results. 

15  6-3.  Answers  to  the  questions — Why  do  these  adaptive 
modifications  in  an  individual  animal,  soon  reach  a  limit? 
and  why,  in  the  descendants  of  "such  animal,  similarly  condi- 
tioned, is  this  limit  very  slowly  extended  ? — are  to  be  found 
in  the  same  direction  as  was  the  answer  to  the  last  question. 
And  here  the  connexion  of  cause  and  consequence  is  much 
more  manifest. 

Since  the  function  of  any  organ  is  dependent  on  the  func- 
tions of  the  organs  which  supply  it  with  materials  and  forces; 
and  since  the  functions  of  these  subsidiary  organs  are  de- 
pendent on  the  functions  of  organs  which  supply  them  wi<  h 
materials  and  forces;  it  follows  that  before  any  great  extra 
power  of  discharging   its    function,    can   be   gained   by    a 


ADAPTATION.  193 

specially- exercised  organ,  a  considerable  extra  power  must 
be  gained  by  a  series  of  immediately-subservient  organs,  and 
Borne  extra  power  by  a  secondary  series  of  remotely-sub- 
servient organs.  Thus  there  are  required  numerous  and 
wide-spread  modifications.  Before  the  artery  which  feeds  a 
hard-worked  muscle,  can  permanently  furnish  a  large  ad- 
ditional quantity  of  blood,  it  must  increase  in  diameter  and 
contractile  power ;  and  that  its  increase  of  diameter  and  con- 
tractile power  may  be  of  use,  the  main  artery  from  which  it 
diverges,  must  also  be  so  far  modified  as  to  bring  this  addi- 
tional quantity  of  blood  to  the  branch  artery.  Similarly 
with  the  veins  ;  similarly  with  the  absorbents ;  similarly 
with  the  nerves.  And  when  we  ask  what  these  subsidiary 
changes  imply,  we  are  forced  to  conclude  that  there  must  be 
an  analogous  group  of  more  numerous  changes,  ramifying 
throughout  the  system.  The  growth  of  the  arteries  prima- 
rily and  secondarily  implicated,  cannot  go  to  any  extent, 
without  growth  in  the  minor  blood-vessels  on  which  their 
nutrition  depends ;  while  their  greater  contractile  power  in- 
volves enlargement  of  the  nerves  which  excite  them,  and 
some  modification  of  that  part  of  the  spinal  cord  whence 
these  nerves  proceed.  Thus,  without  tracing  the  like  remote 
alterations  implied  by  extra  growth  of  the  veins,  absorbents, 
and  other  agencies,  it  is  manifest  that  a  large  amount  of  re- 
building must  be  done  throughout  the  organism,  before  any 
organ  of  importance  can  be  permanently  increased  in  size 
and  power  to  a  great  extent.  Hence,  though  such  extra 
growth  in  any  part  as  does  not  necessitate  considerable 
changes  throughout  the  rest  of  the  organism,  may  rapidly 
take  place  ;  a  further  growth  in  this  part,  requiring  a  re- 
modelling of  numerous  parts  remotely  and  slightly  affected, 
must  take  place  but  slowly. 

\Ve  have  before  found  our  conceptions  of  vital  processes 
made  clearer  by  studying  analogous  social  processes.  In 
societies  there  is  a  mutual  dependence  of  functions,  essentially 
like  that  which  exists  in  organisms;  and  there  is  also  an 


L94  THE    INDUCTIONS   OF    BIOLOGY. 

essentially  like  re-action  of  functions  on  structures.  From  tLe 
laws  of  adaptive  modification  in  societies,  we  may  therefore 
hope  to  get  a  clue  to  the  laws  of  adaptive  modification  in 
organisms.  Let  us  suppose,  then,  that  a  society  has  arrived 
at  a  state  of  equilibrium  like  that  of  a  mature  animal — a 
state  not  like  our  own,  in  which  growth  and  structural  de- 
velopment are  rapidly  going  on ;  but  a  state  of  settled 
balance  among  the  functional  powers  of  the  various  classes 
and  industrial  bodies,  and  a  consequent  fixity  in  the  relative 
sizes  of  such  classes  and  bodies.  Further,  let  us  suppose 
that  in  a  society  thus  balanced,  there  occurs  something  which 
throws  an  unusual  demand  on  some  one  industry — say  an 
unusual  demand  for  ships  (which  we  will  assume  to  be  built 
of  iron)  in  consequence  of  a  competing  mercantile  nation 
having  been  prostrated  by  famine  or  pestilence.  The  imme- 
diate result  of  this  additional  demand  for  iron  ships,  is  the 
employment  of  more  workmen,  and  the  purchase  of  more  iron, 
by  the  ship-builders ;  and  when,  presently,  the  demand  con- 
tinuing, the  builders  find  their  premises  and  machinery  in- 
sufficient, they  enlarge  them.  If  the  extra  requirement 
persists,  the  high  interest  and  high  wages  bring  such  extra 
capital  and  labour  into  the  business,  as  are  needed  for  new 
ship-building  establishments.  But  such  extra  capital  and 
labour  do  not  come  quickly  ;  since,  in  a  balanced  community, 
not  increasing  in  population  and  wealth,  labour  and  capital 
have  to  be  drawn  from  other  industries,  where  they  are 
already  yielding  the  ordinary  returns.  Let  us  now  go  a 
step  further.  Suppose  that  this  iron-ship-building  industry, 
having  enlarged  as  much  as  the  available  capital  and  labour 
permit,  is  still  unequal  to  the  demand ;  what  limits  its  im- 
mediate further  growth  ?  The  lack  of  iron.  By  the  hypo- 
thesis, the  iron-producing  industry,  like  all  the  other  indus- 
tries throughout  the  community,  yields  only  as  much  iron  as 
is  habitually  required  for  all  the  purposes  to  which  iron  is 
applied :  ship-building  being  only  one.  If,  then,  extra  iron 
id  required  for  ship-building,  the  first  effect  is  to  withdraw 


ADAPTATION  195 

part  of  the  iron  habitually  consumed  for  other  purposes,  and 
lo  raise  the  price  of  iron.  Presently,  the  iron-makers  feel 
this  change,  and  their  stocks  dwindle.  As,  however,  tho 
quantity  of  iron  required  for  ship-building,  forms  but  a  small 
part  of  the  total  quantity  required  for  all  purposes  ;  the  ex- 
tra demand  on  the  iron-makers,  can  be  nothing  like  so  great 
in  proportion  as  is  the  extra  demand  on  the  ship- builders. 
Whence  it  follows,  that  there  will  be  much  less  tendency  to 
an  immediate  enlargement  of  the  iron-producing  industry — 
the  extra  quantity  will  for  some  time  be  obtained  by  working 
extra  hours.  Nevertheless,  if,  as  fast  as  more  iron  can  be 
thus  supplied,  the  ship-building  industry  goes  on  growing 
— if,  consequently,  the  iron-makers  experience  a  permanently- 
increased  demand,  and  out  of  their  greater  profits  get  higher 
interest  on  capital,  as  well  as  pay  higher  wages ;  there  will 
eventually  be  an  abstraction  of  capital  and  labour  from  other 
industries,  to  enlarge  the  iron-producing  industry :  new  blast- 
furnaces, new  rolling-mills,  new  cottages  for  workmen,  will 
be  erected.  But  obviously,  the  inertia  of  capital  and  labour 
to  be  overcome,  before  the  iron-producing  industry  can  grow 
by  a  decrease  of  some  other  industries,  will  prevent  its  growth 
from  taking  place  until  long  after  the  increased  ship-build- 
ing industry  has  demanded  it ;  and  meanwhile,  the  growth 
of  the  ship-building  industry  must  be  limited  by  the 
deficiency  of  iron.  A  remoter  restraint  of  the  same  nature, 
meets  us  if  we  go  a  step  further — a  restraint  which  can 
be  overcome,  only  in  a  still  longer  time.  For  the  manu- 
facture of  iron  depends  on  the  supply  of  coal.  The  pro- 
duction of  coal  being  previously  in  equilibrium  with  the 
consumption  ;  and  the  consumption  of  coal  for  the  manu- 
factuie  of  iron,  being  but  a  small  part  of  the  total  con- 
sumption ;  it  follows  that  a  considerable  extension  of  the  iron 
manufacture,  when  it  at  length  takes  place,  will  cause  but  a 
comparatively  small  additional  demand  on  the  coal-owners  and 
coal-miners — a  demand  which  will  not,  for  a  long  period,  suf- 
fice to  cause  enlargement  of  the  coal- trade,  by  drawing  capital 


196  THE    INDUCTIONS    OF    BIOLOGY. 

and  labour  from  other  investments  and  occupations.  And 
until  the  permanent  extra  demand  for  coal,  has  become  great 
enough  to  draw  from  other  investments  and  occupations,  suf- 
ficient capital  and  labour  to  sink  new  mines,  the  increasing 
production  of  iron  must  be  restricted  by  the  scarcity  of  coal ; 
and  the  multiplication  of  ship-yards  and  ship-builders, 
must  be  checked  by  the  want  of  iron.  Thus,  in  a  com- 
munity which  has  reached  a  state  of  moving  equilibrium, 
though  any  one  industry  directly  affected  by  an  additional 
demand,  may  rapidly  undergo  a  small  extra  growth ; 
yet  a  growth  beyond  this,  requiring,  as  it  does,  the  build- 
ing-up of  subservient  industries,  less  directly  and  strongly 
affected,  as  well  as  the  partial  wwbuilding  of  other  industries, 
can  take  place  only  with  comparative  slowness.  And  a 
still  further  growth,  requiring  structural  modifications  of 
industries  still  more  distantly  affected,  must  take  place  still 
more  slowly. 

Returning  from  this  analogy,  we  realize  more  clearly  the 
truth,  that  any  considerable  member  of  an  animal  organism, 
cannot  be  greatly  enlarged  without  some  general  re-organiza- 
tion. Besides  a  building-up  of  the  primary,  secondary,  and 
tertiary  groups  of  subservient  parts,  there  must  be  an  un- 
building  of  sundry  non-subservient  parts  ; — or  at  any  rate, 
there  must  be  permanently  established,  a  lower  nutrition  of 
6uch  non-subservient  parts.  For  it  must  be  remembered  that 
in  a  mature  animal,  or  one  which  has  reached  a  balance 
between  assimilation  and  expenditure,  there  cannot  be  an  in- 
crease in  the  nutrition  of  some  organs,  without  a  decrease  in 
the  nutrition  of  others  ;  and  an  organic  establishment  of  the 
increase,  implies  an  organic  establishment  of  the  decrease — 
implies  more  or  less  change  in  the  processes  and  structures 
throughout   the    entire   system.  And   here,   in- 

,  deed,  is  disclosed  one  reason  why  growing  animals  under- 
go adaptations  so  much  more  readily  than  adult  ones.  For 
while  there  is  surplus  nutrition,  it  is  possible  for  specially-ex- 
ercijed  parts  to  be  specially  enlarged,  without  any  positive 


ADAPTATION.  197 

deduction  from  other  parts.  There  is  required  only  that 
negative  deduction,  shown  in  the  diminished  growth  of  other 
parts. 

§  70.  Pursuing  the  argument  further,  we  reach  an  ex- 
planation of  the  third  general  truth  ;  namely,  that  organisms, 
and  species  of  organisms,  which,  under  new  conditions,  have 
undergone  adaptive  modifications,  soon  return  to  something 
like  their  original  structures,  when  restored  to  their  original 
conditions.  Seeing,  as  we  have  done,  how  excess  of  action 
and  excess  of  nutrition  in  any  part  of  an  organism,  must 
affect  action  and  nutrition  in  subservient  parts,  and 
these  again  in  other  parts,  until  the  re-action  has  divided 
and  subdivided  itself  throughout  the  organism,  affecting 
in  decreasing  degrees  the  more  and  more  numerous  parts 
more  and  more  remotely  implicated ;  we  see  that  the 
consequent  changes  in  the  parts  remotely  implicated,  consti- 
tuting the  great  mass  of  the  organism,  must  be  extremely 
slow.  Hence,  if  the  need  for  the  adaptive  modification 
ceases,  before  the  great  mass  of  the  organism  has  been  much 
altered  in  its  structure  by  these  ramified  but  minute  re-ac- 
tions; we  shall  have  a  condition  in  which  the  specially- 
modified  part,  is  not  in  equilibrium  with  the  rest.  All  the 
i-emotely-affected  organs,  as  yet  but  little  changed,  will,  in  the 
absence  of  the  perturbing  cause,  resume  very  nearly  their 
previous  actions.  The  parts  that  depend  on  them,  will 
consequently  by  and  by  do  the  same.  Until  at  length,  by  a 
reversal  of  the  adaptive  process,  the  organ  at  first  affected  will 
be  brought  back  almost  to  its  original  state.  Recon- 

sidering the  above-drawn  analogy  between  an  organism  and 
society,  will  enable  us  better  to  realize  this  necessity.  If,  in 
the  case  supposed,  the  extra  demand  for  iron  ships,  after 
causing  the  erection  of  some  additional  ship-yards  and  the 
drawing  of  iron  from  other  manufactures,  were  to  cease  ; 
the  old  dimensions  of  the  ship-building  trade  would  be 
quickly  returned  to:  discharged  workmen  would  seek  fresh 


198  THE    INDUCTIONS    OF    BIOLOGY. 

occupations,  and  the  new  yards  would  be  devoted  to  othei 
uses.  But  if  the  increased  need  for  ships  lasted  long 
enough,  and  became  great  enough,  to  cause  a  flow  of  capital 
and  labour  from  other  industries  into  the  iron-manufacture,  a 
falling  off  in  the  demand  for  ships,  would  much  less  rapidly 
entail  a  dwindling  of  the  ship-building  industry.  For  iron 
being  now  produced  in  greater  quantity,  a  diminished  con- 
sumption of  it  for  ships,  would  cause  a  fall  in  its  price,  and 
a  consequent  fall  in  the  cost  of  ships :  thus  enabling  the 
ship-builders  to  meet  the  competition  which  we  may  sup- 
pose led  to  a  decrease  in  the  orders  they  received.  And  since, 
when  new  blast-furnaces  and  rolling-mills,  &c,  had  been  built 
with  capital  drawn  from  other  industries,  its  transference 
back  into  other  industries,  would  involve  great  loss ;  the 
owners,  rather  than  transfer  it,  would  accept  unusually  low  in- 
terest ;  and  an  excess  of  iron  would  continue  to  be  produced ; 
resulting  in  an  undue  cheapness  of  ships,  and  a  maintenance 
of  the  ship-building  industry  at  a  size  beyond  the  need. 
Eventually,  however,  if  the  number  of  ships  required  still 
diminished,  the  pioduction  of  iron  in  excess  would  become 
very  unremunerative  :  some  of  the  blast-furnaces  would  be 
blown  out ;  and  as  much  of  the  capital  and  labour  as  remained 
available,  would  be  re-distributed  among  other  occupations. 
Without  repeating  the  steps  of  the  argument,  it  will  be  clear 
that  were  the  enlargement  of  the  ship-building  industry 
great  enough,  and  did  it  last  long  enough,  to  cause  an  in- 
crease in  the  number  of  coal-mines  ;  the  ship-building  in- 
dustry would  be  still  better  able  to  maintain  itself  under 
adverse  circumstances ;  but  that  it  would,  though  at  a  more 
distant  period,  end  by  sinking  down  to  the  needful  dimensions. 
Thus  our  conclusions  are  : — First,  that  if  the  extra  activity 
and  growth  of  a  particular  industry,  has  lasted  long  enough 
onlv  to  remodel  the  proximately- affected  industries ;  it  will 
dwindle  away  again  after  a  moderate  period,  if  the  need  for 
it  disappears.  Second,  that  an  enormous  period  must  be  re- 
quired before  the  re-actions  produced  by  an  enlarged  industry 


ADAPTATION.  199 

can  cause  a  re-construction  of  the  whole  society,  and  before 
the  countless  re-distributions  of  capital  and  labour,  can  again 
reach  a  state  of  equilibrium.  And  third,  that  only  when 
such  a  new  state  of  equilibrium  is  eventually  reached,  can  the 
adaptive  modification  become  a  permanent  one.  How, 

in  animal  organisms,  the  like  argument  will  hold,  needs  not 
be  pointed  out.     The  reader  will  readily  follow  the  parallel. 

That  organic  types  should  be  comparatively  stable^  might 
be  anticipated  on  the  hypothesis  of  Evolution.  If  we  assume, 
as  we  must  according  to  this  hypothesis,  that  the  structure 
of  any  organism  is  a  product  of  the  almost  infinite  series  of 
actions  and  re-actions  to  which  all  ancestral  organisms  have 
been  exposed  ;  we  shall  see  that  any  unusual  actions  and  re- 
actions brought  to  bear  on  an  individual,  can  have  but 
an  infinitesimal  effect  in  permanently  changing  the  structure 
of  the  organism  as  a  whole.  The  new  set  of  forces,  com- 
pounded with  all  the  antecedent  sets  of  forces,  can  but  inap- 
preciably modify  that  moving  equilibrium  of  functions  which 
all  these  antecedent  sets  of  forces  have  established.  Though 
there  may  result  a  considerable  perturbation  of  certain  func- 
tions— a  considerable  divergence  from  their  ordinary  rhythms; 
yet  the  general  centre  of  equilibrium  cannot  be  sensibly 
changed.  On  the  removal  of  the  perturbing  cause,  the  pre- 
vious balance  will  be  quickly  restored :  the  effect  of  the  new 
forces  being  almost  obliterated  by  the  enormous  aggregate  of 
forces  which  the  previous  balance  expresses. 

§  71.  As  thus  understood,  the  phenomena  of  adaptation 
full  into  harmony  with  first  principles.  The  inference  that 
organic  types  are  fixed,  because  the  deviations  from  them 
which  can  be  produced  within  assignable  periods,  are  relatively 
small ;  and  because,  when  a  force  producing  deviation  ceases, 
there  is  a  return  to  something  like  the  original  state ;  proves  to 
be  an  invalid  inference.  Without  assuming  fixity  of  species, 
we  find  good  reasons  for  anticipating  that  kind  and  degree  of 
stability  which  is  observed.    We  find  grounds  for  concluding, 


200  THE    INDUCTIONS   OF    BIOLOGY. 

a  priori,  that  an  adaptive  change  of  structure,  will  soon  reach 
a  point  beyond  which  further  adaptation  will  be  slow ;  for 
concluding  that  when  the  modifying  cause  has  been  but 
a  short  time  in  action,  the  modification  generated,  will  be 
evanescent ;  for  concluding  that  a  modifying  cause  acting 
even  for  many  generations,  will  do  but  little  towards  per- 
manently altering  the  organic  equilibrium  of  a  race ; 
and  for  concluding  that  on  the  cessations  of  such  cause,  its 
eifects  will  become  unapparent  in  the  course  of  a  few  gener- 
ations. 


CHAPTER  VI. 
INDIVIDUALITY. 

§  72.  What  is  an  individual  ?  is  a  question  which  many 
readers  will  think  it  easy  to  answer.  Yet  it  is  a  question 
that  has  led  to  much  controversy  among  Zoologists  and 
Botanists  ;  and  no  quite  satisfactory  reply  to  it  seems  possi- 
ble. As  applied  to  a  man,  or  to  any  one  of  the  higher 
animals,  which  are  all  sharply-defined  and  independent,  the 
word  individual  has  a  clear  meaning ;  though  even  hero, 
when  we  turn  from  average  cases  to  exceptional  cases — 
as  a  calf  with  two  heads  and  two  pairs  of  fore-limbs — we 
find  ourselves  in  doubt  whether  to  predicate  one  individuality 
or  two.  But  when  we  extend  our  range  of  observation  to 
the  organic  world  at  large,  we  find  that  difficulties  allied  to 
this  exceptional  one,  meet  us  everywhere  under  every  variety 
of  form. 

Each  uniaxial  plant  may  perhaps  fairly  be  regarded  as  a 
distinct  individual ;  though  there  are  botanists  who  do  not 
make  even  this  admission.  What,  however,  are  we  to  say  of 
a  raultiaxial  plant  ?  It  is,  indeed,  usual  to  speak  of  a  tree 
with  its  many  branches  and  shoots,  as  singular ;  but  strong 
reasons  may  be  urged  for  considering  it  as  plural.  Every 
one  of  its  axes  has  a  more  or  less  independent  life,  and  when 
cut  off  and  planted,  may  grow  into  the  likeness  of  its  parent; 
ov  by  grafting  and  budding,  parts  of  this  tree  may  be 
developed  upon  another  tree,  and  there  manifest  their 
14 


202  THE    INDUCTIONS    OF    BIOLOGY. 

specific  peculiarities.  Shall  we  regard  all  the  growing  axes 
thus  resulting  from  slips  and  grafts  and  buds,  as  parts  of  one 
individual,  or  as  distinct  individuals  ?  If  a  strawberry-plant 
sends  out  runners  carrying  buds  at  their  ends,  which  strike 
root  and  grow  into  independent  plants,  that  separate  from 
the  original  one  by  decay  of  the  runners,  must  we  not  say 
that  they  possess  separate  individualities  ;  and  yet  if  we  do 
this,  are  we  not  at  a  loss  to  say  when  their  separate  individu- 
alities were  established,  unless  we  admit  that  each  bud  was 
from  the  beginning  an  individual  ?  Commenting  on  such 
perplexities,  Schleiden  says — "  Much  has  been  written  and 
disputed  concerning  the  conception  of  the  individual,  with- 
out, however,  elucidating  the  subject,  principally  owing  to 
the  misconception  that  still  exists  as  to  the  origin  of  the  con- 
ception. Now  the  individual  is  no  conception,  but  the  mere 
subjective  comprehension  of  an  actual  object,  presented  to  us 
under  some  given  specific  conception,  and  on  this  latter  it 
alone  depends  whether  the  object  is  or  is  not  an  individual. 
Under  the  specific  conception  of  the  solar  system,  ours  is  an 
individual :  in  relation  to  the  specific  conception  of  a  planet- 
ary body,  it  is  an  aggregate  of  many  individuals."  *  *  *  "I 
think,  however,  that  looking  at  the  indubitable  facts 
already  mentioned,  and  the  relations  treated  of  in  the  course  of 
these  considerations,  it  will  appear  most  advantageous  and 
most  useful,  in  a  scientific  point  of  view,  to  consider  the 
vegetable  cell  as  the  general  type  of  the  plant  (simple  plant 
of  the  first  order).  Under  this  conception,  Protococcus  and 
other  plants  consisting  of  only  one  cell,  and  the  spore  and 
pollen- granule,  will  appear  as  individuals.  Such  individuals 
may,  however,  again,  with  a  partial  renunciation  of  their  in- 
dividual independence,  combine  under  definite  laws  into 
definite  forms  (somewhat  as  the  individual  animals  do  in  the 
globe  of  the  Volvox  globator*).  These  again  appear  empiri- 
cally as  individual  beings,  under  a  conception  of  a  species 

«  It  is  now  generally  agreed  thai  the  Volvox  globator  is  a  plant. 


INDIVIDUALITY. 


203 


(simple  plants  of  the  second  order)  derived  from  the  form  of 
the  normal  connexion  of  the  elementary  individuals.  But 
we  cannot  stop  here,  since  nature  herself  combines  these  in- 
dividuals, under  a  definite  form,  into  larger  associations, 
whence  we  draw  the  third  conception  of  the  plant,  from  a 
connexion,  as  it  were,  of  the  second  power  (compound  plants 
— plants  of  the  third  order).'  The  simple  plant  proceeding 
from  the  combination  of  the  elementary  individuals  is  then 
termed  a  bud  (gemma),  in  the  composition  of  plants  of  the 
third  order." 

The  animal  kingdom  presents  still  greater  difficulties. 
When,  from  sundry  points  on  the  body  of  a  common  polype, 
there  bud-out  young  polypes,  which,  after  acquiring  mouths 
and  tentacles  and  closing  up  the  communications  between 
their  stomachs  and  the  stomach  of  the  parent,  finally  separate 
from  the  parent ;  we  may  with  propriety  regard  them  as  dis- 
tinct individuals.  But  when,  in  the  allied  compound  Hydro- 
zoa,  we  find  that  these  young  polypes  continue  permanently 
connected  with  the  parent ;  and  when,  by  this  continuous 
budding-out,  there  is  presently  produced  a  tree-like  aggre- 
gation, having  a  common  alimentary  canal  into  which  the 
digestive  cavity  of  each  polype  opens;  it  is  no  longer  so 
clear  that  these  little  sacs  furnished  with  mouths  and  tenta- 
cles, are  severally  to  be  regarded  as  distinct  individuals.  We 
cannot  deny  a  certain  individuality  to  the  polypedom.  And 
on  discovering  that  some  of  the  buds,  instead  of  unfolding  in 
the  same  manner  as  the  rest,  are  transformed  into  capsules 
in  which  eggs  are  developed — on  discovering  that  certain  of 
the  incipient  polypes  thus  become  wholly  dependent  on  the 
aggregate  for  their  nutrition,  and  discharge  functions  which 
have  nothing  to  do  with  their  own  maintenance,  we  have 
still  clearer  proof  that  the  individualities  of  the  members  are 
partially  merged  in  the  individuality  of  the  group.  Other 
organisms  belonging  to  the  same  order,  display  still  more 
decidedly  this  transition  from  simple  individualities  to  a  com- 
plex individuality.     In  the  Diplujes  there  is  a  special  modifi- 


^04  THE    INDUCTIONS   OF    BIOLOGY. 

cation  of  one  or  more  members  of  the  polypcdom  into  a 
swimming  apparatus,  which,  by  its  rhythmical  contractions, 
propels  itself  through  the  water,  drawing  the  polypedom  after 
it.  And  in  the  more  differentiated  Physalin,  various  organs 
result  from  the  metamorphosis  of  parts  that  are  the  honio- 
logues  of  individual  polypes.  In  this  last  instance,  the  in- 
dividuality of  the  aggregate  is  so  predominant,  that  the 
individualities  of  the  members  are  practically  lost.  This 

combination  of  individualities  in  such  way  as  to  produce  a 
composite  individual,  meets  us  in  other  forms  among  the 
ascidian  molluscs.  While  in  some  of  these,  as  in  the 
Clavelina,  the  animals  associated  are  but  little  subordinated 
to  the  community  they  form  ;  in  others,  as  in  the  Botryllidce, 
they  are  so  fused  into  a  rounded  mass,  as  to  present  the 
appearance  of  a  single  animal  with  several  mouths  and 
stomachs. 

On  the  hypothesis  of  Evolution,  perplexities  of  this  nature 
are  just  such  as  we  might  anticipate.  If  Life  in  general,  com- 
menced with  minute  and  simple  forms,  like  those  out  of 
which  all  individual  organisms,  however  complex,  now 
originate  ;  and  if  the  transitions  from  these  primordial  units 
to  organisms  made  up  of  groups  of  such  units,  and  to  higher 
organisms  made  up  of  groups  of  such  groups,  took  place  by 
degrees ;  it  is  clear  that  individualities  of  the  first  and 
simplest  order,  would  merge  gradually  in  those  of  a  larger 
and  more  complex  order,  and  these  again  in  others  of  an 
order  having  still  greater  bulk  and  organization ;  and  that 
hence  it  would  be  impossible  to  say  where  the  lower  indivi- 
dualities ceased,  and  the  higher  individualities  commenced. 

§  73.  To  meet  these  difficulties,  it  has  been  proposed  that 
the  whole  product  of  a  single  fertilized  germ,  shall  be  re- 
garded as  a  single  individual :  whether  such  whole  product 
be  organized  into  one  mass,  or  whether  it  be  organized  into 
many  masses,  that  are  partially  or  completely  separate.  It 
is  urged  that  whether  the  development  of  the  fertilized  germ 


INDIVIDUALITY.  205 

bo  continuous  or  discontinuous  (§  50)  is  a  matter  of  secondary 
importance ;  that  the  totality  of  living  tissue  to  which  the 
fertilized  germ  gives  rise  in  any  one  case,  is  the  equivalent 
of  the  totality  to  which  it  gives  rise  in  any  other  case ;  and 
that  we  must  recognize  this  equivalence,  whether  such  totality 
of  living  tissue  takes  a  concrete  or  a  discrete  arrangement. 
In  pursuance  of  this  view,  a  zoological  individual  is  consti- 
tuted either  by  any  such  single  animal  as  a  mammal  or  bird, 
which  may  properly  claim  the  title  of  a  zoon,  or  by  any  such 
group  of  animals  as  the  numerous  Medusa  that  have  been 
developed  from  the  same  egg,  which  are  to  be  severally  dis- 
tinguished as  zooids. 

Admitting  it  to  be  very  desirable  that  there  should  be 
words  for  expressing  these  relations  and  this  equivalence,  it 
may  still  be  objected,  that  to  apply  the  word  individual  to  a 
number  of  separate  living  bod  ies,  is  inconvenien  t :  conn ictingso 
much,  as  it  does,  with  the  ordinary  conception  which  this  word 
suggests.  It  seems  a  questionable  use  of  language  to  say  that 
the  countless  masses  of  Anacharts  Alsinastrum,  which,  within 
these  few  years,  have  grown  up  in  our  rivers,  canals,  and 
ponds,  are  all  parts  of  one  individual ;  and  yet  as  this  plant 
does  not  seed  in  England,  these  countless  masses,  having 
arisen  by  discontinuous  development,  must  be  so  regarded,  if 
we  accept  the  above  definition. 

It  may  be  contended,  too,  that  while  it  does  violence  to 
our  established  way  of  thinking,  this  mode  of  interpreting 
the  facts  is  not  without  its  difficulties — smaller,  perhaps, 
than  those  it  escapes,  but  still  considerable.  Something 
seems  to  be  gained  by  restricting  the  application  of  the  title 
individual,  to  organisms  which,  being  in  all  respects  fully 
developed,  possess  the  power  of  producing  their  kind  after 
the  ordinary  sexual  method;  and  denying  this  title  to  those 
incomplete  organisms  which  have  not  this  power.  But  the 
definition  does  not  really  establish  this  distinction  for  us.  On 
the  one  hand,  Ave  have  cases  in  which,  as  in  the  working  bee, 
the  whole  of  the  germ-product  is  aggregated  into  a  single 


206  THE    INDUCTIONS    OF    BIOLOGY. 

organism ;  and  yet,  though  an  individual  according  to  the 
definition,  this  organism  has  no  power  of  reproducing  its 
kind.  On  the  other  hand,  we  have  cases  like  that  of  the 
perfect  Aphides,  where  the  organism  is  but  an  infinitesimal 
part  of  the  germ-product ;  and  yet  has  that  completeness 
required  for  sexual  reproduction.  Moreover,  if  we 

adopt  the  proposed  view,  we  find  ourselves  committed  to  the 
anomalous  position,  that  among  many  orders  of  animals,  there 
are  no  concrete  individuals  at  all.  If  the  individual  is  consti- 
tuted by  the  whole  germ-product,  whether  continuously  or 
discontinuously  developed,  then,  not  only  must  individuality 
be  denied  to  each  of  the  imperfect  Aphides,  but  also  to 
each  of  the  perfect  males  and  females ;  since  no  one  of 
them  is  more  than  a  minute  fraction  of  the  total  germ- 
product.  And  yet  further,  it  might  be  urged  with 
some  show  of  reason,  that  if  the  conception  of  individuality 
involves  the  conception  of  completeness  ;  then,  an  organism 
which  possesses  an  independent  power  of  reproducing  itself, 
being  more  complete  than  an  organism  in  which  this  power 
is  dependent  on  the  aid  of  another  organism,  is  more  in- 
dividual. 

§  74.  There  is,  indeed,  as  already  implied,  no  definition 
of  individuality  that  is  unobjectionable.  All  we  can  do  is  to 
make  the  best  practicable  compromise. 

As  applied  either  to  an  animate  or  an  inanimate  object, 
the  word  individual  ordinarily  connotes  union  among  the 
parts  of  the  object,  and  separateness  from  other  objects. 
This  fundamental  element  in  the  conception  of  individuality, 
we  cannot  with  propriety  ignore  in  the  biological  application 
of  the  word.  That  which  we  call  an  individual  plant  or  animal, 
must,  therefore,  be  some  concrete  whole,  and  not  a  discrete 
whole.  If,   however,    we    say   that   each   concrete 

living  whole  is  to  be  regarded  as  an  individual,  we  are  still 
met  by  the  question — What  constitutes  a  concrete  living 
whole  ?     A  young  organism  arising  by  internal  or  externa] 


INDIVIDUALITY.  207 

gemmation  from  a  parent  organism,  passes  gradually  from  a 
state  in  which  it  is  an  indistinguishable  part  of  the  parent 
organism,  to  a  state  in  which  it  is  a  separate  organism  of  like 
structure  with  the  parent.  At  what  stage  does  it  become  an 
individual  ?  And  if  its  individuality  be  conceded  only  when 
it  completely  separates  from  the  parent,  must  we  deny  in- 
dividuality to  all  organisms  thus  produced,  which  permanently 
retain  their  connexions  with  their  parents  ?  Or  again,  what 
must  we  say  of  the  Hcctocotylus,  which  is  an  arm  of  the 
Cuttle-fish  that  undergoes  a  special  development,  and  then 
detaching  itself,  lives  independently  for  a  considerable 
period  ?  And  what  must  we  say  of  that  larval  Echinus, 
which  is  left  to  move  about  awhile  after  being  robbed  of  its 
viscera  by  the  young  Echinus  developed  within  it  ? 

To  answer  such  questions,  we  must  revert  to  the  definition 
of  Life.  The  distinction  between  individual  in  its  biological 
6ense,  and  individual  in  its  more  general  sense,  must  consist 
in  the  manifestation  of  Life,  properly  so  called.  Life  we 
have  seen  to  be,  "  the  definite  combination  of  heterogeneous 
changes,  both  simultaneous  and  successive,  in  correspondence 
with  external  co-existences  and  sequences."  Hence,  a  biolo- 
gical individual  is  any  concrete  whole  having  a  structuro 
which  enables  it,  when  placed  in  appropriate  conditions,  to 
continuously  adjust  its  internal  relations' to  external  relations, 
so  as  to  maintain  the  equilibrium  of  its  functions.  In 

pursuance  of  this  conception,  we  must  consider  as  individuals, 
all  those  wholly  or  partially  independent  organized  masses, 
which  arise  by  multicentral  and  multiaxial  development  that 
is  either  continuous  or  discontinuous  (§  50).  We  must 
accord  the  title  to  each  separate  aphis,  each  polype  of  a 
polypedom,  each  bud  or  shoot  of  a  flowering  plant,  whether 
it  detaches  itself  as  a  bulbil  or  remains  attached  as  a  branch. 

By  thus  interpreting  the  facts,  we  do  not,  indeed,  avoid  all 
anomalies.  While,  among  flowering  plants,  the  power  of  in- 
dependent growth  and  development,  is  usually  possessed  only 
by  shoots  or  axes  ;  yet,  in  some  cases,  as  in  that  of  the  Begonia- 


208  THE   INDUCTIONS   OF   BIOLOGY. 

leaf  awhile  since  mentioned,  the  appendage  of  an  axis,  or  even 
a  small  fragment  of  such  appendage,  is  capable  of  initiating 
and  carrying  on  the  functions  of  life ;  and  in  other  cases,  as 
shown  by  M.  Naudin  in  the  Droscra  intermedia,  young 
plants  are  occasionally  developed  from  the  surfaces  of  leaves, 
while  still  connected  with  the  parent  plant.  Nor  among 
forms  like  the  compound  Hydrozoa,  does  the  definition 
enable  us  to  decide  where  the  line  is  to  be  drawn  between 
the  individuality  of  the  group  and  the  individualities  of  the 
members — merging  into  each  other,  as  these  do,  in  different 
degrees.  But,  as  before  said,  such  difficulties  must  necessa- 
rily present  themselves,  if  organic  forms  have  arisen  by  in- 
sensible gradations.  We  must  be  content  with  a  course 
which  commits  us  to  the  smallest  number  of  incongruities ; 
and  this  course  is,  to  consider  as  an  individual,  any  centre  or 
axis  that  is  capable  of  independently  carrying  on  that  con- 
tinuous adjustment  of  inner  to  outer  relations  which  consti- 
tutes Life. 


CHAPTER   VII. 
GENESIS. 

§  75.  Ha\ing  concluded  what  constitutes  an  individual, 
we  are  in  a  position  to  deal  with  the  multiplication  of  in- 
dividuals. For  this,  the  title  Genesis  is  here  chosen,  as  being 
the  most  comprehensive  title — the  least  specialized  in  its 
meaning.  By  some  biologists,  Generation  has  been  used  to 
signify  one  method  of  multiplication,  and  Reproduction  to 
signify  another  method  ;  and  each  of  these  words  has  been 
thus  rendered  in  some  degree  unfit  to  signify  multiplication 
in  general. 

Here  the  reader  is  indirectly  introduced  to  the  fact,  that 
the  production  of  new  organisms  is  carried  on  in  fundament- 
ally unlike  ways.  Up  to  quite  recent  times,  it  was  believed, 
even  by  naturalists,  that  all  the  various  processes  of  multipli- 
cation observable  in  different  kinds  of  organisms,  have  one 
essential  character  in  common  :  it  was  supposed  that  in  every 
species,  the  successive  generations  arc  alike.  It  has  now  been 
proved,  however,  that  in  plants,  and  in  numerous  animals,  the 
successive  generations  are  not  alike  ;  that  from  one  generation 
there  proceeds  another  whose  members  differ  more  or  less 
in  structure  from  their  parents  ;  that  these  produce  others 
like  themselves,  or  like  their  parents,  or  like  neither ;  but 
that  eventually,  the  original  form  re-appears.  Instead  of 
there  being,  as  in  the  cases  most  familiar  to  us,  a  constant 
recurrence  of  the  same  form,  there  is  a  cyclical  recurrence  of 


210  THE    INDUCTIONS    OF    BIOLOGY. 

the  same  form.  These  two  distinct  processes  of  multiplication, 
may  be  aptly  termed  homogenesis  and  heterogenesis*  Under 
these  heads  let  us  consider  them  more  closely. 

The  kind  of  genesis,  once  supposed  to  be  universal,  in 
which  the  successive  generations  are  alike,  is  always  sexual 
genesis  ;  or,  as  it  has  been  otherwise  called — gamogenesis.  In 
every  species  of  organism  which  multiplies  by  homogenesis, 
each  generation  consists  of  males  and  females  ;  and  from  the 
fertilized  germs  they  produce,  the  next  generation  of  similar 
males  and  females  arises.  This  method  of  propagation  is 
further  distinguished  by  the  peculiarity,  that  each  fertilized 
germ  gives  rise  to  but  one  individual — the  product  of  de- 
velopment is  always  organized  round  one  axis,  and  not  round 
several  axes.  .Between  the  different  kinds  of  homo- 

genesis,  the  most  marked  contrast,  and  the  only  one  which 
need  here  detain  us,  is  that  between  the  oviparous  and  the 
viviparous.  The  oviparous  kind  is  that  in  which  the  fertil- 
ized germ  is  detached  from  the  parent,  before  it  has 
undergone  any  considerable  development.  The  viviparous 
kind  is  that  in  which  development  is  considerably  advanced, 
or  almost  completed,  before  final  detachment  takes  place. 
This  distinction  is,  however,  not  a  sharply- denned  one:  there 
are  transitions  between  the  oviparous  and  the  viviparous 
processes.  In  ovo-viviparous  genesis,  thei*e  is  an  internal 
incubation  ;  and  though  the  young  are  in  this  case  finally 
detached  from  the  parent  in  the  shape  of  eggs,  they  do  not 
leave  the  parent's  body  until  after  they  have  assumed 
something    like    the    parental    form.  Looking 

around,  we  find  that  homogenesis  is  universal  among  the 
Vertebrata  :  there  is  no  known  vertebrate  animal  but  what 
arises  from  a  fertilized  germ,  and  unites  into  its  single  indi- 
viduality  the  whole  products   of   this  fertilized  germ.     In 

*  Unfortunately  the  word  heierc  genesis,  has  been  already  used  as  a  synoiiymt 
for  "  spontaneous  generation."  Save  by  those  few  who  believe  in  "  sponteueoua 
generation,"  however,  little  objection  will  be  felt  to  using  the  word  in  a  seaac 
that  seems  much  more  appropriate. 


GE3NESIS.  211 

the  mammals  or  highest  Vertebrata,  this  homogenesis  is  in 
every  case  viviparous ;  in  birds  it  is  uniformly  oviparous ; 
and  in  reptiles  and  fishes,  it  is  always  essentially  oviparous, 
though  there  are  cases,  of  the  kind  above  referred  to,  in 
which  viviparity  is  simulated.  Passing  to  the  Invertebrate, 
we  find  oviparous  homogenesis  universal  among  the  Arach- 
nida  (except  the  Scorpions,  which  are  ovo-viviparous) ; 
universal  among  the  higher  Crustacea,  but  not  among 
the  lower ;  extremely  general,  though  not  universal,  among 
Insects  ;  and  universal  among  the  higher  Mollusca,  though 
not  among  the  lower.  Along  with  extreme  inferiority  among 
animals,  we  find  homogenesis  to  be  the  exception  rather 
than  the  rule  ;  and  in  the  vegetal  kingdom,  there  appear  to 
be  no  cases,  save  those  of  a  few  aberrant  parasites  like  the 
Rafflesiacca;,  in  which  the  centre  or  axis  which  arises  from  a 
fertilized  germ,  becomes  the  immediate  producer  of  fertilized 
germs. 

Where  propagation  is  carried  on  by  heterogenesis,  or  is 
characterized  by  unlikeness  of  the  successive  generations, 
there  is  always  asexual  genesis  with  occasionally-recurring 
sexual  genesis ;  in  other  words — agamogenesis  interrupted 
more  or  less  frequently  by  gamogencsis.  If  we  set  out  with 
a  generation  of  perfect  males  and  females ;  then,  from  their 
ova  or  seeds,  there  arise  individuals  that  are  neither  males 
nor  females,  but  that  produce  the  next  generation  from 
buds.  By  this  method  of  multiplication,  many  individuals 
originate  from  a  single  fertilized  germ :  the  product  of 
development  is  organized  round  more  than  one  centre  or 
axis.  The  simplest  form  of  heterogenesis  is  that 

seen  in  uniaxial  plants.  If,  as  we  find  ourselves  obliged  to 
do,  we  regard  each  separate  shoot  or  axis  of  growth,  as  a  dis- 
tinct individual ;  then,  in  uniaxial  plants,  the  successive  in- 
dividuals are  not  represented  by  the  series  A,  A,  A,  A,  &c, 
like  those  resulting  from  homogenesis  ;  but  they  are  repre- 
sented by  the  series  A,  B,  A,  B,  A,  B,  &c.  For  in  plants 
which  were  before  classed  as  uniaxial  (§  50),  and  which  may 


212  THE    INDUCTIONS   OF    BIOLOGY. 

be  conveniently  so  distinguished  from  other  plants,  the  axis 
which  shoots  up  from  the  seed,  and  substantially  constitutes 
the  plant,  does  not  itself  flower  and  bear  seed ;  but  gives  lateral 
origin  to  flowering,  or  seed -bearing,  axes.  Though  in  uni- 
axial plants,  the  fructifying  apparatus  appears  to  be  at  the  end 
of  the  primary,  vertical  axis ;  yet  dissection  shows  that, 
morphologically  considered,  each  fructifying  axis  is  usually 
an  offspring  from  the  primary  axis.  There  arises  from  the  seed, 
a  sexless  individual,  from  which  spring  by  gemmation,  in- 
dividuals having  reproductive  organs ;  and  from  these  there 
result  fertilized  germs  or  seeds,  that  give  rise  to  sexless 
individuals.  That  is  to  say,  gamogenesis  and  agamogenesis 
alternate  :  the  peculiarity  being,  that  the  sexual  individu- 
als arise  from  the  sexless  ones  by  continuous  development. 
The  Salpce  show  us  an  allied  form  of  heterogenesis  in 
the  animal  kingdom.  Individuals  developed  from  fertilized 
ova,  instead  of  themselves  producing  fertilized  ova,  produce, 
by  gemmation,  strings  of  individuals ;  from  which  fertilized 
ova  again  originate.  In  multiaxial  plants,  we  have 

a  succession  of  generations  represented  by  the  series  A,  B, 
B,  B,  &c,  A,  B,  B,  B,  &c.  Supposing  A  to  be  a  flowering 
axis,  or  sexual  individual ;  then,  from  any  fertilized  germ  it 
casts  off,  there  grows  up  a  sexless  individual,  B  ;  from  this 
there  bud-out  other  sexless  individuals,  B ;  and  so  on  for 
generations  more  or  less  numerous  ;  until  at  length,  from 
some  of  these  sexless  individuals,  there  bud-out  seed-bearing 
individuals  of  the  original  form  A.  Branched  herbs, 
shrubs,  and  trees,  exhibit  this  form  of  heterogenesis :  the 
successive  generations  of  sexless  individuals  thus  produced, 
being  in  most  cases  continuously  developed,  or  aggregated 
into  a  compound  individual ;  but  being  in  some  cases  dis- 
continuously  developed.  Among  animals,  a  kind  of  hetero- 
genesis represented  by  the  same  succession  of  letters,  occurs 
in  such  compound  polypes  as  the  Sertularia;  and  in 
those  of  the  Hydrozoa  which  assume  alternately  the  poly- 
poid form,  and  the  form  of  the  Medusa :  the  chief  differences 


GENESIS.  213 

presented  by  these  groups,  arising  from  the  fact  that  the 
successive  generations  of  sexless  individuals  produced  by 
budding,  are  in  some  cases  continuously  developed,  and  in 
others  discontinuously  developed ;  and  from  the  fact  that,  in 
some  cases,  the  sexual  individuals  give  off  their  fertilized 
germs  while  still  growing  on  the  parent-polypedom,  but  in 
other  cases,  not  until  after  leaving  the  parent-polypedom  and 
undergoing  further  development.  Where,  as  in  all 

the  foregoing  kinds  of  agamogenesis,  the  new  individuals 
bud-out,  not  from  any  specialized  reproductive  organs,  but 
from  unspecialized  parts  of  the  parent ;  the  process  has  been 
named,  by  Prof.  Owen,  metagenesis.  In  most  instances,  the 
individuals  thus  produced,  grow  from  the  outsides  of  the 
parents — the  metagenesis  is  external.  But  there  is  also  a 
kind  of  metagenesis  which  we  may  distinguish  as  internal. 
Certain  entozoa  of  the  genus  Distoma,  exhibit  it.  From  the 
egg  of  a  Distoma,  there  results  a  rudely-formed  creature 
known  to  naturalists  as  the  "  King's-yellow  worm."  Gradu- 
ally as  this  increases  in  size,  the  greater  part  of  its  inner 
substance  is  transformed  into  young  animals  called  Cercarice 
(which  are  the  larva3  of  Distomata)  ;  until  at  length,  it 
becomes  little  more  than  a  living  sac,  full  of  living  offspring. 
In  the  Distoma  pacijica,  the  brood  of  young  animals  thus 
arising  by  internal  gemmation,  are  not  Cercarice,  but  are  of 
tbe  same  form  as  their  parent :  themselves  becoming  the 
producers  of  Cercarice  after  the  same  manner,  at  a  subsequent 
period.  So  that  sometimes  the  succession  of  forms  is  repre- 
sented by  the  series  A,  B,  A,  B,  &c.  ;  and  sometimes  by  the 
series  A,  B,  B,  A,  B,  B,  &c.  Both  cases,  however,  exemplify 
internal  metagenesis,  in  contrast  with  the  several  kinds  of 
external  metagenesis  described  above.  That  agamo- 

genesis which  is  carried  on  in  a  reproductive  organ — either 
a  true  ovarium  or  the  homologue  of  one — has  been  called,  by 
Prof.  Owen,  parthenogenesis.  In  his  work  published  under 
tbis  title,  he  embraced  those  cases  in  which  the  buds  arising 
in  the  pseud- ovarium,  are  not  ova  in  the  full  sense  of  the 


214:  THE    INDUCTIONS   OF    BIOLOGY. 

Word ;  but  rather,  as  they  have  since  been  called  by  Prof. 
Huxley,  pseud-ova.  Yon  Siebold  and  other  naturalists,  have 
hence  applied  the  term  parthenogenesis  to  a  narrower  class 
cf  cases.  Perhaps  it  would  be  best  to  distinguish  this 
process,  which  is  intermediate  between  metagenesis  anr1 
parthenogenesis,  by  the  term  pseudo-parthenogenesis.  It 
is  the  process  familiarly  exemplified  in  the  Aphides. 
Here,  from  the  fertilized  eggs  laid  by  perfect  females,  there 
grow  up  imperfect  females,  in  the  pseud-ovaria  of  which 
there  are  developed  pseud-ova  ;  and  these,  rapidly  assuming 
the  organization  of  other  imperfect  females,  are  born  vivi- 
parously.  From  this  second  generation  of  imperfect  females, 
there  by  and  by  arises,  in  the  same  manner,  a  third  genera- 
tion, of  the  same  kind ;  and  so  on  for  many  generations  :  the 
series  being  thus  symbolized  by  the  letters  A,  B,  B,  B,  B, 
B,  &c,  A.  Pespecting  this  kind  of  heterogenesis,  it  should 
be  added,  that  in  animals,  as  in  plants,  the  number  of  genera- 
tions of  sexless  individuals  produced  before  the  re-appearance 
of  sexual  ones,  is  indefinite  ;  both  in  the  sense  that  in  the 
same  species  it  may  go  on  to  a  greater  or  less  extent  accord- 
ing to  circumstances,  and  in  the  sense  that  among  the  genera- 
tions of  individuals  proceeding  from  the  same  fertilized  germ, 
a  recurrence  of  sexual  individuals  takes  place  earlier  in  some 
of  the  diverging  lines  of  multiplication  than  in  others.  In 
trees  we  see  that  on  some  branches,  flower-bearing  axes  arise 
while  other  branches  are  still  producing  only  leaf-bearing 
axes  ;  and  in  the  successive  generations  of  Aphides,  a  parallel 
truth  has  been  observed.  Lastly  has  to  be  set  down, 

that  form  of  heterogenesis  in  which,  along  with  gamogenesis, 
there  occurs  a  form  of  agamogenesis  exactly  like  it,  save  in  tho 
absence  of  fecundation.  This  is  called  true  parthenogenesis — 
reproduction  carried  on  by  virgin  mothers,  which  are  in  all 
respects  like  other  mothers.  In  the  silk-worm-moths 
this  parthenogenesis  is  exceptional,  rather  than  ordinary  : 
usually  the  eggs  of  these  insects  are  fertilized ;  but  if  they 
are  not,  they  are  still  laid,  and  some  of  them  produce  larva). 
In  certain  Lepidoptcra,  however,  of  the  groups  Psychidce.  and 


GENESIS. 


!lo 


Tiiicidfc,  parthenogenesis  appears  to  be  a  normal  process — 
indeed,  so  far  as  is  known,  the  only  process  ;  for  of  some 
species  the  males  have  never  been  found. 

A  general  conception  of  the  relations  among  the  different 
modes  of  Genesis,  thus  briefly  described,  will  be  best  given 
by  the  following  tabular  statement. 


Homogencsis,  which  is  Gamogenesis    - 


Genesis  is- 


'  Oviparous 

or 
Ovo-viviparouo 

or 
w  Viviparous 


.  HetcrogenesiSj'vvliich  is 


f  Gamogenesis 
alternating 
with 
Agamogenesis 


'  Parthenogenesis 

or 
Pseudo-parthenogenesir 
or  r  Internal 

Metagenesis  1        or 

[External 


This,  like  all  other  classifications  of  such  phenomena,  pre- 
sents anomalies.  It  may  be  justly  objected,  that  the  processes 
here  grouped  under  the  head  agamogenesis,  are  the  same  as 
those  before  grouped  under  the  head  of  discontinuous  develop- 
ment (§  50)  :  thus  making  development  and  genesis  partially 
coincident.  Doubtless  it  seems  awkward  that  what  are  from 
one  point  of  view  considered  as  structural  changes,  are  from 
another  point  of  view  considered  as  modes  of  multiplication.* 

*  Prof.  Huxley  avoids  this  difficulty  by  making  every  kind  of  Genesis  a  mode 
of  development.     His  classification,  which  suggested  the  one  given  above,  is  at 

follows : — 


'Continuous 


Development 


(  Growth 

(  Metamorphosis 


Discontinuous    \ 


I  Agamogenesis  { 


/  Metagenesis 


'  Gamogenesis 


( Parthenogenesis 


21G  THE   INDUCTIONS    OF    BIOLOGY. 

There  is,  hoAvever,  nothing  for  us  but  a  choice  of  imperfec- 
tions. We  cannot  by  any  logical  dichotomies,  accurately 
express  relations  which,  in  Nature,  graduate  into  each  other 
insensibly.  Neither  the  above,  nor  any  other  scheme,  can  do 
more  than  give  an  approximate  idea  of  the  truth. 

§  76.  Genesis  under  every  form,  is  a  process  of  negative 
or  positive  disintegration  ;  and  is  thus  essentially  opposed  to 
that  process  of  integration,  which  is  one  element  of  individual 
evolution.  Negative  disintegration  occurs  in  those  cases 
where,  as  among  the  compound  Hydrozoa,  there  is  a  con- 
tinuous development  of  new  individuals  by  budding  from  the 
bodies  of  older  individuals  ;  and  where  the  older  individuals 
are  thus  prevented  from  growing  to  a  greater  size,  or  reach- 
ing a  higher  degree  of  integration.  Positive  disintegration 
occurs  in  those  cases  of  agamogenesis  where  the  formation 
of  new  individuals  is  discontinuous,  and  in  all  cases  of  gamo- 
genesis.  The  degrees  of  disintegration  are  various.  At 
the  one  extreme,  the  parent  organism  is  completely  broken 
up,  or  dissolved  into  new  individuals  ;  and  at  the  other 
extreme,  the  new  individual  forms  but  a  small  deduction 
from  the  parent  organism.  Protozoa  and  Protophyta,  show 
us  that  form  of  disintegration  called  spontaneous  fission : 
two  or  four  individuals  being  produced  by  the  splitting-up 
of  the  original  one.  The  Volcox  and  the  Hydrodidyon, 
are  plants  which,  having  developed  broods  of  young  plants 
within  themselves,  give  them  exit  by  bursting ;  and  among 
animals,  the  one  lately  referred  to,  which  arises  from  the 
Distoma  egg,  entirely  loses  its  individuality  in  the  individ- 
ualities of  the  numerous  Distonia-larYXs  with  which  it  be- 
comes filled.  Speaking  generally,  the  degree  oi 
disintegration  becomes  less  marked,  as  we  approach  the  higher 
organic  forms.  Plants  of  advanced  types  throw  off  from 
themselves,  whether  by  gamogenesis  or  agamogenesis,  parts 
that  are  relatively  small ;  and  among  the  higher  animals, 
there  is  no  case  in  which  the  parent  individuality  is  habitually 


GENESIS.  217 

lost,  in  the  production  of  new  individualities.  To  the 

last,  however,  there  is  of  necessity  a  greater  or  less  disinte- 
gration. The  seeds  and  pollen-grains  of  a  flowering  plant, 
are  disintegrated  portions  of  tissue ;  as  are  also  the  ova  and 
spermatozoa  of  animals.  And  whether  the  fertilized  germs 
carry  away  from  their  parents  small  or  large  quantities  of 
nutriment,  these  quantities  of  nutriment  in  all  cases  involve 
further  negative  or  positive  disintegrations  of  the  parents. 

New  individuals  that  result  from  agamogenesis,  usually  do 
not  separate  from  the  parent-individuals,  until  they  have 
undergone  considerable  development,  if  not  complete  develop- 
ment. The  agamogenetic  offspring  of  those  lowest  organisms 
which  develop  centrally,  do  not,  of  course,  pass  beyond  cen- 
tral structure ;  but  the  agamogenetic  offspring  of  organisms 
that  develop  axially,  commonly  assume  an  axial  structure 
before  they  become  independent.  The  vegetal  kingdom  shows 
us  this  in  the  advanced  organization  of  detached  bulbils,  and 
of  buds  that  root  themselves  before  separating.  Of  animals, 
the  Hydrozoa,  the  Trematoda,  the  Salpce,  and  the  Aphides, 
present  us  with  different  kinds  of  agamogenesis,  in  all  of 
which  the  new  individuals  are  organized  to  a  considerable 
extent  before  being  cast  off.  This  rule  is  not  without  excep- 
tions, however.  The  winter-eggs  of  the  Plitmatella,  developed 
in  an  unspecialized  part  of  the  bod)'-,  present  us  with  a  case 
of  metagenesis,  in  which  centres  of  development,  instead  of 
axes,  are  detached ;  and  in  the  above-described  parthenogene- 
sis of  moths  and  bees,  such  centres  are  detached  from  an 
ovarium. 

When  produced  by  gamogenesis,  the  new  individuals  be- 
come independent  of  the  parents  while  in  the  shape  of  centres 
of  development,  rather  than  axes  of  development ;  and  this 
even  where  the  reverse  is  apparently  the  case.  The  fertilized 
germs  of  those  inferior  plants  which  are  central,  or  multicen- 
tral,  in  their  development,  are  of  course  thrown  off  as  centres. 
In  the  higher  plants,  of  the  two  elements  that  go  to  the  form- 
ation of  the  fertilized  germ,  the  pollen-cell  is  absolutely 
15 


218  THE   INDUCTIONS    OF    BIOLOGY. 

separated  from  the  parent-plant  under  the  shape  of  a  centre : 
and  the  embryo-cell,  though  not  absolutely  separated  from 
the  parent,  is  still  no  longer  subordinate  to  the  organizing 
forces  of  the  parent.  So  that  when,  the  embryo- cell  having 
been  fertilized  by  matter  from  the  pollen-tube,  the  develop- 
ment commences,  it  proceeds  without  parental  control  : 
the  new  individual,  though  remaining  physically  united 
with  the  old  individual,  becomes  structurally  and  functionally 
separate  while  still  only  a  centre  of  development ;  and  takes 
on  its  axial  form  by  processes  of  its  own — the  old  individual 
doing  no  more  than  supply  materials.  Through- 

out the  animal  kingdom,  the  new  individuals  produced  by 
gamogenesis,  are  obviously  separated  in  the  shape  of  centres 
of  development  wherever  the  reproduction  is  oviparous .  the 
only  conspicuous  variation  being  in  the  quantity  of  nutritive 
matter  bequeathed  by  the  parent  to  the  new  centre  of  de- 
velopment, at  the  time  of  its  separation.  And  though,  where 
the  reproduction  is  viviparous,  the  process  appears  to  be 
different,  and  in  one  sense  is  so ;  yet,  intrinsically,  it  is  the 
same.  For  in  these  cases,  the  new  individual  really  detaches 
itself  from  the  parent  while  still  only  a  centre  of  develop- 
ment ;  but  instead  of  being  finally  cast  off  in  this  state,  it  is 
re-attached,  and  supplied  with  nutriment  until  it  assumes  a 
more  or  less  complete  axial  structure. 

§  77.  Under  all  its  various  forms,  the  essential  act  in  gamo- 
genesis, is  the  union  of  two  centres  or  cells,  produced  by 
different  parent  organisms :  the  sperm-cell  being  the  male 
product,  and  the  germ-cell  the  female.  There  are  very 
many  modes  and  modifications  of  modes  in  which  these 
cells  are  produced ;  very  many  modes  and  modifications  of 
modes  by  which  they  are  brought  into  contact ;  and  very 
many  modes  and  modifications  of  modes  by  which  the  result- 
ing fertilized  germs  have  secured  to  them  the  fit  conditions 
for  their  development.  But  passing  over  these  many  diver- 
gent and  re-divergent  kinds  of  sexual  multiplication,  which 


GENESIS.  219 

t  would  take  too  much  space  here  to  specify,  the  one  uni- 
versal peculiarity  which  it  concerns  us  to  remark,  is,  this  co- 
alescence of  a  detached  portion  of  one  organism,  with  a  more 
or  less  detached  portion  of  another. 

Such  protophytes  as  the  Palmellce  and  the  Dcstnidicm, 
which  are  sometimes  distinguished  as  unicellular  plants,  show 
us  a  coalescence,  not  of  detached  portions  of  two  organisms, 
but  of  two  entire  organisms  :  in  the  Palmellce,  conjugation  is 
a  complete  fusion  of  the  individuals  ;  and  in  the  Dcsmidiece, 
the  entire  contents  of  the  individuals  unite  to  form  the  germ- 
mass.  Where,  as  among  the  Confervce,  we  have  aggregated 
cells  whose  individualities  are  scarcely  at  all  subordinate  to 
that  of  the  aggregate,  the  gamogenetic  act  is  effected  by  the 
union  of  the  contained  granules  of  two  adjacent  cells.  In 
Spirogyra,  it  is  not  adjacent  cells  in  the  same  thread  which 
thus  combine  ;  but  cells  of  one  thread  with  those  of  another. 
As  we  ascend  to  plants  of  high  organization,  we  find  that; 
the  two  reproductive  elements  become  quite  distinct  in 
their  characters ;  and  further,  that  they  arise  in  different 
organs  set  apart  for  their  production  :  the  arrangements 
being  such,  that  the  sperm-cells  of  one  plant  combine  with 
the  germ -cells  of  another. 

There  is  reason  to  think  that,  among  the  lowest  Protozoa, 
a  fusion  of  two  individualities,  analogous  to  that  which  occurs 
in  the  conjugation  of  certain  Algce,  is  the  process  from  which 
results  the  gerni  of  a  new  series  of  individuals.  But  in 
animals  formed  by  the  aggregation  of  units  that  are  homolo- 
gous with  Protozoa,  the  sperm-cells  and  germ-cells  are  differ- 
entiated. And  even  in  these  humble  forms,  where  there  is  no 
differentiation  of  sexes,  we  have  good  evidence  that,  as  in  all 
higher  forms,  the  union  is  not  between  sperm-cells  and  germ- 
cells  that  have  arisen  in  the  same  individual ;  but  between 
those  that  have  arisen  in  different  individuals. 

The  marvellous  phenomena  initiated  by  the  meeting  of 
sperm-cell  and  germ-cell,  naturall)'  suggest  the  conception  of 
some  quite  special  and  peculiar  properties  possessed  by  thcoe 


t 


220  THE    INDUCTIONS   OF    BIOLOGY. 

cells.  It  seems  obvious  that  this  mysterious  power  which 
they  display,  of  originating  a  new  and  complex  organism, 
distinguishes  them  in  the  broadest  way  from  portions  of  organio 
substance  in  general.  Nevertheless,  the  more  we  study  the 
evidence,  the  more  is  this  assumption  shaken — the  more  are 
we  led  towards  the  conclusion,  that  these  cells  have  not 
been  made  by  some  unusual  elaboration,  fundamentally 
different  from   all  other  cells.  The  first  fact  which 

points  to  this  modified  conclusion,  is  the  fact  recently  dwelt 
upon  (§  68),  that  in  many  plants  and  inferior  animals,  a 
small  fragment  of  tissue  that  is  but  little  differentiated,  is 
capable  of  developing  into  the  form  of  the  organism  from 
which  it  was  taken.  Conclusive  proof  obliged  us  to  admit, 
that  the  component  units  of  organisms,  have  inherent  powers 
of  arranging  themselves  into  the  forms  of  the  organisms  to 
which  they  belong.  And  if  to  these  component  units,  which 
we  distinguished  as  physiological,  such  powers  must  be  con- 
ceded— if,  under  fit  conditions,  and  when  not  much  specialized, 
they  manifest  such  powers  in  a  way  as  marked  as  that  in 
which  the  contents  of  sperm-cells  and  germ-cells  manifest 
them ;  then,  it  becomes  clear  that  the  properties  of  sperm- 
cells  and  germ-cells  are  not  so  peculiar  as  we  are  apt  to 
assume.  Again,  the  organs  for  preparing  sperm- 

cells  and  germ-cells,  have  none  of  the  speciality  of  struc- 
ture which  might  be  looked  for,  did  sperm-cells  and  germ- 
cells  need  endowing  with  properties  essentially  unlike 
those  of  all  other  organic  agents.  On  the  contrary,  these 
reproductive  centres  proceed  from  tissues  that  are  character- 
ized by  their  low  organization.  In  plants,  for  example,  it  is 
not  appendages  that  have  acquired  considerable  structure, 
which  produce  the  fructifying  particles  :  these  arise  at  the 
extremities  of  the  axes,  where  the  degree  of  structure  is  the 
least.  The  embryo-cells  are  formed  in  the  undifferentiated 
part  of  the  cambium-layer  ;  the  pollen-grains  are  formed  at 
the  little-differentiated  extremities  of  the  stamens ;  and  both 
&re  homologous  with  simple  epithelium- cells.     Among  manv 


GXMSSI8.  221 

inferior  animals  devoid  of  special  reproductive  organs,  such 
as  the  Hydra,  the  ova  and  spermatozoa  originate  in  the 
layer  of  indifferent  tissue  that  lies  between  the  endoderm 
and  the  ectoderm  ;  that  is,  they  consist  of  portions  of  the 
least  specialized  substance.  And  in  the  higher  animals, 
these  same  generative  agents  appear  to  be  merely  modified 
epithelium-cells — cells  not  remarkable  for  their  complexity 
of  structure,  but  rather  for  their  simplicit}>\  If,  by 

way  of  demurrer  to  this  view,  it  is  asked  why  other  epithe- 
lium-cells do  not  exhibit  like  properties ;  there  are  two  replies. 
The  first  is,  that  other  epithelium-cells  are  usually  so  far 
changed  to  fit  them  to  their  special  functions,  that  they  are 
unfitted  for  assuming  the  reproductive  function.  The  second 
reply  is,  that  in  some  cases,  where  the  epithelium- cells  are 
but  very  little  specialized,  they  do  exhibit  the  like  properties : 
not,  indeed,  by  uniting  with  other  epithelium-cells  to  produce 
new  germs,  but  by  producing  new  germs  without  such  union. 
I  learn  from  Dr  Hooker,  that  the  Begonia  phyllomaniaca 
habitually  develops  young  plants  from  the  scales  of  its  stem 
and  leaves — nay,  that  many  young  plants  are  developed  by  a 
single  scale.  The  epithelium-cells  composing  one  of  these 
scales,  swell,  here  and  there,  into  large  globular  cells ;  form 
chlorophyll  in  their  interiors ;  shoot  out  rudimentary  axes ; 
and  then,  by  spontaneous  constrictions,  cut  themselves  off; 
drop  to  the  ground  ;  and  grow  into  Begonias.  It  appears, 
too,  that  in  a  succulent  English  plant,  the  Malaxis  paludosa, 
a  like  process  occurs :  the  self-detached  celk  being,  in  this 
case,  produced  by  the  surfaces  of  the  leaves.  Thus, 

there  is  no  warrant  for  the  assumption  that  sperm-cells  and 
germ-cells  possess  powers  fundamentally  unlike  those  of 
other  cells.  The  inference  to  which  the  facts  point,  is,  that 
they  differ  from  the  rest,  mainly  in  not  having  undergone 
modifications  such  as  those  by  which  the  rest  are  adapted  to 
particular  functions.  They  are  cells  that  have  departed  but 
little  from  the  original  and  most  general  type.  Or,  in  the 
words  suggested  by  a  friend,  it  is  not  that  they  are  peculiar!) 


222  THE    INDUCTIONS   OF    BIOLOGY. 

specialized,  but  rather  that  they  are  unspecialized  :  such 
specializations  as  some  of  them  exhibit  in  the  shape  of  loco- 
motive appliances,  &c,  being  interpretable  not  as  intrinsic, 
but  as  extrinsic,  modifications,  that  have  reference  to  nothing 
beyond  certain  mechanical  requirements.  Sundry 

facts  tend  likewise  to  show,  that  there  does  not  exist  the  pro- 
found distinction  which  we  are  apt  to  assume,  between  the 
male  and  female  reproductive  elements.  In  the  common 
polype,  sperm-cells  and  germ-cells  are  developed  in  the  same 
layer  of  indifferent  tissue  ;  and  in  Tethya,  one  of  the  sponges, 
Prof.  Huxley  has  observed  that  they  occur  mingled  together 
in  the  general  parenchyma.  The  pollen-grains  and  embryo- 
cells  of  plants,  arise  in  adjacent  parts  of  the  cambium-layer  ; 
and  from  a  description  of  a  monstrosity  in  the  Passion-flower, 
recently  given  by  Mr  Salter  to  the  Linnncan  Society,  it  ap- 
pears, both  that  ovule3  may,  in  their  general  structure, 
graduate  into  anthers,  and  that  they  may  produce  pollen  in 
their  interiors.  All  which  evidence  is  in  perfect  harmony 
with  the  foregoing  conclusion ;  since,  if  sperm-cells  and 
germ-cells  have  natures  not  essentially  unlike  those  of  un- 
specialized  cells  in  general,  their  natures  cannot  be  essen- 
tially unlike  each  other. 

The  next  general  fact  to  be  noted,  is,  that  these  cells 
whose  union  constitutes  the  essential  act  of  gamogenesis,  are 
cells  in  which  the  developmental  changes  have  come  to  a 
close — cells  which,  however  favourably  circumstanced  in 
respect  of  nutrition,  are  incapable  of  further  evolution. 
Though  they  are  not,  as  many  cells  are,  unfitted  for  growth 
and  metamorphosis  by  being  highly  specialized;  yet  they 
have  lost  the  power  of  growth  and  metamorphosis.  They 
have  severally  reached  a  state  of  equilibrium.  And  while 
the  internal  balance  of  forces  prevents  a  continuance  of  con- 
structive changes,  it  is  readily  overthrown  by  external 
destructive  forces.  For  it  uniformly  happens  that  sperm- 
cells  aud  germ-cells  which  are  not  brought  in  contact,  disap- 
pear.      In    a   plant,  the   embryo-cell,    if  not   fertilized,   is 


GENESIS.  223 

absorbed  or  dissipated,  while  the  ovule  aborts;  and  the  un- 
impregnated  ovum  eventually  decomposes. 

Such  being  the  characters  of  these  cells,  and  such  being 
their  fates  if  kept  apart,  we  have  now  to  observe  what  hap- 
pens when  they  are  united.  For  a  long  time,  the  immediate 
sequence  of  their  contact  was  not  ascertained.  This  is  at 
length,  however,  decided.  It  has  been  shown  that  in  plants, 
the  extremity  of  the  elongated  pollen-cell  applies  itself  to  tho 
surface  of  the  embryo-sac,  but  does  not  enter  the  embryo- 
sac.  In  animals,  however,  the  process  is  different.  Careful 
observers  agi'ee,  that  the  spermatozoon  passes  through  the 
limiting  membrane  of  the  ovum.  The  result  in  both  cases  is 
presumed  to  be  a  mixture  of  the  contents  of  the  two 
cells.  The  evidence  goes  to  show  that  in  plants,  matter 
passes  by  osmose  from  the  pollen-cell  into  the  embryo- 
cell  ;  and  that  in  animals,  the  substance  contained  in  the 
spermatozoon  becomes  mingled  with  the  substance  contained 
in  the  ovum,  either  by  simple  diffusion  or  by  cell-multiplica- 
tion. But  the  important  fact  which  it  chiefly  con- 
cerns us  to  notice,  is,  that  on  the  union  of  these  reproductive 
elements,  there  begins,  either  at  once  or  on  the  return  of 
favourable  conditions,  a  new  series  of  developmental  changes. 
The  state  of  equilibrium  at  which  each  of  them  had  arrived, 
is  destroyed  by  their  mutual  influence  ;  and  the  constructive 
changes  which  had  come  to  a  close,  recommence :  a  process 
of  cell-multiplication  is  set  up ;  and  the  resulting  cells  pre- 
sently begin  to  aggregate  into  the  rudiment  of  a  new 
organism. 

Thus,  passing  over  the  variable  concomitants  of  ganio- 
genesis,  and  confining  our  attention  to  what  is  constant  in  it, 
we  see  : — that  there  is  habitually,  if  not  universally,  a  fusion 
of  two  portions  of  organic  substance,  which  are  either  them- 
selves distinct  individuals,  or  are  thrown  off  by  distinct 
individuals ;  that  these  portions  of  organic  substance,  which 
are  severally  distinguished  by  their  low  degree  of  special- 
ization, have  arrived  at  states  of  structural  quiescence  or 


224  THE    INDUCTIONS    OF    BIOLOGY. 

equilibrium  ;  that  if  they  are  not  united,  this  equilibrium 
ends  in  dissolution ;  but  that  by  the  mixture  of  them,  thie 
equilibrium  is  destroyed,  and  a  new  evolution  initiated. 

§  78.  What  are  the  conditions  under  which  Genesis  takes 
place  ?  How  does  it  happen  that  some  organisms  multiply 
by  homogenesis,  and  others  by  heterogenesis  ?  Why  is  it 
that  where  agamogenesis  prevails,  it  is  usually  from  time  to 
time  interrupted  by  gamogenesis  ?  These  are  questions  of 
extreme  interest ;  but  questions  to  which  decisive  answers 
cannot  yet  be  given.  In  the  existing  state  of  Biology,  we 
must  be  content  if  we  can  learn  the  direction  in  which 
answers  lie.  A  survey  of  the  facts,  discloses  certain  correla- 
tions which,  if  not  universal,  are  too  general  to  be  without 
significance. 

Where  the  multiplication  of  individuals  is  carried  on  by 
heterogenesis,  we  find,  in  numerous  cases,  that  agamogenesis 
continues  as  long  a3  the  forces  which  result  in  growth,  are 
greatly  in  excess  of  the  antagonistic  forces.  While  conversely, 
we  find  that  the  recurrence  of  gamogenesis,  takes  place  when 
the  conditions  are  no  longer  so  favourable  to  growth.  In 
like  manner,  where  there  is  homogenetic  multiplication,  new 
individuals  are  usually  not  formed  while  the  preceding  in- 
dividuals are  still  rapidly  growing — that  is,  while  the  forces 
producing  growth  exceed  the  opposing  forces  to  a  great  extent,- 
but  the  formation  of  new  individuals  begins  when  nutrition 
is  nearly  equalled  by  expenditure.  To  specify  all  the  facts 
uhat  seem  to  warrant  these  inductions,  would  take  more  space 
than  can  be  here  spared.     A  few  of  them  must  suffice. 

The  relation  between  fructification  and  innutrition,  among 
plants,  was  long  ago  asserted  by  a  German  biologist — by 
Wolff,  I  am  told.  When,  some  years  ago,  I  met  with  the 
assertion,  I  was  not  acquainted  with  the  evidence  on  which  it 
rested.  Since  that  time,  however,  I  have,  when  occasion 
favoured,  examined  into  the  facts  for  myself.  The  result  has 
been   a  conviction,  strengthened  by  every  further  inquiry, 


GENESIS. 


225 


that  such  a  relation  exists.  Uniaxial  plants  begin  to 

produce  their  lateral,  flowering  axes,  only  after  the  main 
axis  has  developed  the  great  mass  of  its  leaves,  and  is  show- 
ing its  diminished  nutrition  by  smaller  leaves,  or  shorter 
internodes,  or  both.  In  multiaxial  plants,  two,  three,  or 
more  generations  of  leaf-bearing  axes,  or  sexless  individuals, 
are  produced  before  any  seed-bearing  individuals  show  them- 
selves. When,  after  this  first  stage  of  rapid  growth  and 
agamogenetic  multiplication,  some  gamogenetic  individuals 
arise,  they  do  so  where  the  nutrition  is  least ; — not  on  the 
main  axis,  or  on  the  secondary  axes,  or  even  on  the  tertiary 
axes ;  but  on  axes  that  are  the  most  removed  from  the 
channels  which  supply  nutriment.  Again,  a  flowering  axis 
is  commonly  less  bulky  than  the  others :  either  much 
shorter,  or,  if  long,  much  thinner,  xind  further,  it  is  an 
axis  of  which  the  terminal  internodes  are  undeveloped :  the 
foliar  organs,  which  instead  of  becoming  leaves  become  sepals, 
and  petals,  and  stamens,  follow  each  other  in  close  succession, 
instead  of  being  separated  bj7  portions  of  the  still-growing 
axis.  Another  group  of  evidences  meets  us,  when 

we  observe  the  variations  of  fruit-bearing  that  accompany 
variations  of  nutrition,  in  the  plant  regarded  as  a  whole, 
besides  finding,  as  above,  that  gamogenesis  commences  only 
when  the  luxuriance  of  early  growth  has  been  somewhat 
checked,  by  the  extension  of  the  remoter  parts  of  the  plant  to 
some  distance  from  the  roots ;  we  find  that  gamogenesis  is 
induced  at  an  earlier  stage  than  usual,  by  checking  the  nutri- 
tion Trees  are  made  to  fruit  while  still  quite  small,  by 
cutting  their  roots,  or  putting  them  in  pots  ;  and  luxuriant 
branches  which  have  had  the  flow  of  sap  into  them  diminished, 
Dy  what  gardeners  call  "  ringing,"  begin  to  produce  flower- 
shoots  instead  of  leaf- shoots.  Moreover,  it  is  to  be  remarked 
that  trees  which,  by  flowering  early  in  the  year,  seem  to 
show  a  direct  relation  between  gamogenesis  and  increasing 
nutrition,  really  do  the  reverse  ;  for  in  such  trees,  the  flower- 
buds  are  formed  in  the  autumn — that  structure  which  deter- 


226  THE    INDUCTIONS   OF    BIOLOGY. 

mines  these  buds  into  sexual  individuals,  is  given  when  the 
nutrition  is  declining.  Conversely,  very  high  nutri- 

tion in  plants,  prevents,  or  arrests,  gamogenesis.  It  is 
notorious  that  unusual  richness  of  soil,  or  too  large  a 
quantity  of  manure,  results  in  a  continuous  production  of 
leaf-bearing,  or  sexless,  shoots.  Besides  being  prevented 
from  producing  sexual  individuals,  by  excessive  nutrition, 
plants  are,  by  excessive  nutrition,  made  to  change  the  sexual 
individuals  they  were  about  to  produce,  into  sexless  ones. 
This  arrest  of  gamogenesis  may  be  seen  in  various  stages. 
The  familiar  instance  of  flowers  made  barren  by  the  trans- 
formation of  their  stamens  into  petals,  shows  us  the  lowest 
degree  of  this  reversed  metamorphosis.  Where  the  petals 
and  stamens  are  partially  changed  into  green  leaves,  the 
return  from  the  gamogenetic  structure  towards  the  agamo- 
genetic  structure,  is  more  marked ;  and  it  is  still  more 
marked  when,  as  occasionally  happens  in  luxuriantly-growing 
plants,  new  flowering  axes,  and  even  leaf-bearing  axes,  grow 
out  of  the   centres   of  flowers.*  The   anatomical 

*  Among  various  examples  of  this  which  I  have  observed,  some  of  the  most 
remarkable  were  among  Foxgloves,  growing  in  great  numbers  and  of  large  size, 
in  a  wood  between  "Whatstandwell  Bridge  and  Crich,  in  Derbyshire.  In  one  case, 
the  lowest  flower  on  the  stem,  contained,  in  place  of  a  pistil,  a  shoot  or  spike  of 
flower-buds,  similar  in  structure  to  the  embryo-buds  of  the  main  spike.  1 
counted  seventeen  buds  on  it ;  of  which  the  first  had  three  stamens,  but  was  other- 
wise normal ;  the  second  had  three ;  the  third,  four ;  the  fourth,  four ;  &c. 
Another  plant,  having  more  varied  monstrosities,  evinced  excess  of  nutrition  with 
equal  clearness.  The  following  are  the  notes  I  took  of  its  structure : — 1st,  or 
lowest  flower  on  the  stem,  very  large ;  calyx  containing  eight  divisions,  one 
partly  transformed  into  a  corolla,  and  another  transformed  into  a  small  bud  with 
bract  (this  bud  consisted  of  a  five-cleft  calyx,  four  sessile  anthers,  a  pistil,  and  a 
rudimentary  corolla) ;  the  corolla  of  the  main  flower,  which  was  complete,  con- 
tained six  stamens,  three  of  them  hearing  anthers,  two  others  being  flattened  and 
coloured,  and  one  rudimentary ;  there  was  no  pistil,  but,  in  place  of  it,  a  large 
bud,  consisting  of  a  three-cleft  calyx,  of  which  two  divisions  were  tinted  at  the 
ends,  an  imperfect  corolla,  marked  internally  with  the  usual  purple  spots  and 
hairs,  three  anthers  sessile  on  this  mal-formed  corolla,  a  pistil,  a  seed-vessei  with 
ovules,  and,  growing  to  it,  another  bud  of  which  the  structure  was  indistinct. 
2r1  flower,  large  ;  calyx  of  seven  divisions,  one  being  transformed  into  a  bud 


GENESIS. 


227 


structure  of  the  sexual  axis,  affords  corroborative  evidence : 
giving  very  much  the  impression,  as  it  does,  of  an  aborted 
sexless  axis.  Besides  lacking  those  internodes  which  the 
leaf- bearing  axis  commonly  possesses,  the  flowering  axis 
differs  by  the  absence  of  rudimentary  lateral  axes.  In  a  leaf- 
bearing  axis,  the  axil  of  every  leaf  usually  contains  a  small 
bud,  which  may  or  may  not  develop  into  a  lateral  axis; 
but  though  the  petals  of  a  flower  are  homologous  with  leaves, 
they  do  not  bear  homologous  buds  at  their  bases.  Ordinarily, 
too,  the  foliar  appendages  of  sexual  axes,  are  much  smaller 
than  those  of  sexless  ones — the  stamens  and  pistils  especially, 
which  are  the  last  formed,  being  extremely  dwarfed  ;  and 
there  is  even  reason  for  thinking  that  the  absence  of  chloro- 
phyll from  the  parts  of  fructification,  is  a  fact  of  like  mean- 
ing. Moreover,  the  formation  of  the  seed-vessel  appears 
to  be  a  direct  consequence  of  arrested  nutrition.  If  a 
gloved- finger  be  taken  to  represent  a  growing  shoot, 
(the  finger  standing  for  the  core  of  the  shoot,  and  the 
glove  for  the  cambium-layer,  in  which  the  process  of 
growth  takes  place) ;  and  if  it  be  supposed  that  there  is  a 
diminished  supply  of  material  for  growth  ;  then,  it  seems 
a  fair  inference,  that  growth  will  first  cease  at  the  apex  of 
the  cambium-layer,  represented  b}r  the  end  of  the  glove- 
finger  ;  and  supposing  growth  to  continue  in  those  parts 
of  the  cambium-layer  that  are  nearer  to  the  supply  of  nutri- 
ment, their  further  longitudinal  extension  will  lead  to  the 
formation  of  a  cavity  at  the  extremity  of  the  shoot,  like  that 
which  results  in  a  glove-finger  when  the  finger  is  partially 
withdrawn  and  the  glove  sticks  to  its  end.    "Whence  it  seems, 

with  bract,  but  much  smaller  than  the  other ;  corolla  large  but  cleft  along  the  top  ; 
six  stamens  with  anthers,  pistil,  and  seed-vessel.  3rd  flower,  large;  six-cleft 
calyx,  cleft  corolla,  with  six  stamens,  pistil,  and  seed-vessel,  with  a  second  pistil 
half  unfolded  at  its  apex.  4th  flower,  large  ;  divided  along  the  top,  six  stamens. 
5th  flower,  large;  corolla  divided  into  three  parts,  six  stamens.  6th  flower, 
large ;  corolla  cleft,  calyx  six- cleft,  the  rest  of  the  flower  normal.  7th,  and  all  sue- 
ooecliiig  flowers,  normal. 


22S  THE    INDUCTIONS   OF    BIOLOGY. 

both  that  this  introversion  of  the  carnbium-layor  may  be 
considered  as  due  to  failing  nutrition,  and  that  the  ovules 
growing  from  its  introverted  surface  (which  would  have  been 
its  outer  surface  but  for  the  defective  nutrition)  are  extremely 
aborted  homologues  of  external  appendages — either  leaves 
or  Literal  axes :  the  essential  organs  of  fructification  thus 
arising  where  the  defective  nutrition  has  reached  its  extreme.* 
To  all  which  let  us  not  forget  to  add,  that  the  sperm -cells  and 
germ-cells  are  formed  at  the  very  ends  of  the  organs  of  fruc- 
tification. 

Those  kinds  of  animals  which  multiply  by  heterogenesis, 
present  us  with  a  parallel  relation  between  the  recurrence  of 
gamogenesis  and  the  recurrence  of  conditions  unfavourable  to 
growth — at  least,  this  is  shown  where  experiments  have 
thrown  light  on  the  connexion  of  cause  and  effect  ; 
namely,  among  the  Aphides.  These  creatures,  hatched  from 
eggs  in  the  spring,  multiply  by  agamogenesis  throughout 
the  summer.  When  the  weather  becomes  cold,  and  plants 
no  longer  afford  abundant  sap,  perfect  males  and  females 
are  produced ;  and  from  gamogenesis  there  result  fertilized 
ova.  But  now  observe  that  beyond  this  evidence,  wo 
have  much  more  conclusive  evidence.  For  it  has  been  shown, 
both  that  the  rapidity  of  the  agamogenesis  is  proportionate 
to  the  warmth  and  nutrition,  and  that  if  the  temperature  and 

«  It  appears  that  botanists  do  not  agree  respecting  the  homologies  of  tho 
ovules:  some  thinking  that  they  are  rudimentary  foliar  organs,  and  others  that 
they  are  rudimentary  axial  organs.  Possibly  the  dispute  will  prove  a  bootless 
one ;  since  there  seems  evidence  that  ovules  may  be  transformed  into  either  ono 
or  the  other.  Mr  Salter's  paper,  lately  referred  to,  shows  that  they  may 
graduate  into  stamens,  which  are  foliar  organs ;  and  the  case  of  the  Foxglove, 
which  I  have  described  above,  shows  that  they  may  develop  into  flower-ouds, 
which  are  axial  organs.  I  would  venture  to  suggest,  that  the  conflicting  evidence 
can  be  reconciled,  only  by  regarding  ovules  as  the  homologues  of  lateral  append- 
ages ;  and  considering  a  lateral  appendage  as  composed  of  a  leaf,  plus  a  rudiment- 
ary axis,  either  of  which  may  abort.  This  is  the  view  which  seems  countenanced 
by  development ;  since,  in  its  first  stage,  a  lateral  bud,  whence  a  lateral  append- 
age arises,  6hows  no  division  into  rudimentary  leaf  and  rudimentary  axis  ;  and 
it  is  to  the  lateral  bud  in  this  first  stage,  that  the  seed-bud  or  ovule  is  horoo- 


GENESIS.  220 

supply  of  food  bo  artificially  maintained,  the  agamogenesis 
continues  through  the  winter.  Nay  more — it  not  only,  under 
these  conditions,  continues  through  one  winter,  but  it  has 
been  known  to  continue  for  four  successive  years :  some 
forty  or  fifty  sexless  generations  being  thus  produced.  And 
those  who  have  investigated  the  matter,  see  no  reason  to 
doubt  the  indefinite  continuance  of  this  agamogenetic  mul- 
tiplication, so  long  as  the  external  requirements  are  duly 
met.  Evidence  of  another  kind,  which  points  very 

distinctly  to  the  same  conclusion,  is  furnished  by  the  hetero- 
genesis  of  the  Daphnia — a  small  crustacean  commonly  known 
as  the  "Water-flea,  which  inhabits  ponds  and  ditches.  From 
the  nature  of  its  habitat,  this  little  creature  is  exposed  to  very 
variable  conditions.  Besides  being  frozen  up  in  winter,  the 
small  bodies  of  water  in  which  it  lives,  are  often  unduly 
heated  by  the  summer  sun,  or  dried  up  by  continued  drought. 
The  circumstances  favourable  to  the  Daphnia' s  life  and 
growth,  being  thus  liable  to  interruptions  which,  in  our  cli- 
mate, have  a  regular  irregularity  of  recurrence ;  we  may,  in 
conformity  with  the  hypothesis,  expect  to  find  both  that  the 
gamogenesis  recurs  along  with  evidence  of  declining  nutri- 
tion, and  that  its  recurrence  is  very  variable.  This  we  do 
find.  From  Mr  Lubbock's  paper  on  the  Daphnia  in  the 
"  Philosophical  Transactions "  for  1857,  and  from  further 
information  which  he  has  been  good  enough  to  furnish  me, 
the  following  general  facts  are  deducible  : — First,  that  in 
each  ovarium,  along  with  the  rudiments  of  agamic  eggs,  or 
eggs  which,  if  developed,  produce  young  by  true  partheno- 
genesis, there  usually,  if  not  alwaj^s,  exists  the  rudiment  of 
un  ephippial  egg ;  which,  from  sundry  evidences,  is  inferred 
to  be  a  sexual  or  gamic  egg.  Second,  that  according  to  cir- 
cumstances, either  agamogenesis  or  gamogenesis  takes  place  ; 
but  that  if  the  agamic  eggs  develop,  the  rudimentary  gamic 
egg  disappears,  or  becomes  absorbed  ;  and  conversely,  if  the 
gamic  egg  develops,  the  agamic  eggs  disappear,  or  are  ab- 
sorbed by  it.    Third,  that  the  brood  of  agamic  eggs  contained 


2u0  THE    INDUCTIONS   OF    BIOLOGY. 

in  each  ovarium,  amounts,  under  favourable  circumstances, 
to  as  many  as  eight  or  nine  ;  while  of  the  gamic  eggs,  only 
one  at  a  time  is  produced  in  each  ovarium,  and  occasionally 
one  of  the  ovaria  produces  none  :  whence  it  follows,  that  as 
the  gamic  egg  is  not  more  than  twice  the  bulk  of  the  agamic 
egg,  the  quantity  of  matter  contained  in  an  agamic  brood,  is 
four  times,  and  occasionally  even  eight  time3,  as  great  as 
that  contained  in  a  gamic  bi'ood.  Thus  the  quantity  of 
nutriment  expended  in  gamogenesis  during  a  given  period 
(making  allowance  for  that  which  goes  to  the  formation  of 
the  ephippium),  is  far  less  than  that  expended  in  agamogenesis 
during  a  like  period.  Seeing,  then,  this  constant  preparation 
for  either  gamic  or  agamic  genesis,  in  a  creature  liable  to 
such  irregular  variations  of  nutrition  ;  and  seeing  that  the 
agamogenesis  implies  by  its  amount,  a  large  excess  of  nutri- 
tion, while  the  gamogenesis  implies  by  its  amount,  a  small 
excess  of  nutrition  ;  we  can  scarcely  doubt  that  the  one  or 
the  other  mode  of  multiplication  occurs,  according  as  the 
external  conditions  are  or  are  not  favourable  to  nutrition. 

Passing  now  to  animals  which  multiply  by  homogenesis — 
animals  in  which  the  whole  product  of  a  fertilized  germ  ag- 
gregates round  a  single  centre  or  axis,  instead  of  round  many 
centres  or  axes  ;  we  see,  as  before,  that  so  long  as  the  con- 
ditions allow  rapid  increase  in  the  mass  of  this  germ-product, 
the  formation  of  new  individuals  by  gamogenesis  does  not 
take  place.  Speaking  generally,  we  find  that  only  when 
growth  is  declining  in  relative  rapidity,  do  perfect  sperm- 
cells  and  germ-cells  begin  to  appear;  and  that  the  fullest 
activity  of  the  reproductive  function,  arises  as  growth  ceases 
— speaking  generally,  we  must  say,  because,  though  tlria 
relation  is  tolerably  definite  in  the  highest  orders  of  animala 
which  multiply  by  gamogenesis,  it  is  less  definite  in  the  lower 
orders.  This  admission  does  not  militate  against  the  hypo- 
thesis, as  it  seems  to  do ;  for  the  indefiniteness  of  the  relation 
occurs  where  the  limit  of  growth  is  comparatively  indefinite. 
Wo  «aw   (§  4G)   that  among  active,  hot-blooded  creatures, 


GENESIS.  231 

Rich  as  mammals  and  birds,  the  inevitable  balancing  of 
assimilation  by  expenditure,  establishes,  for  each  species,  an 
almost  uniform  adult  size  ;  -  and  among  creatures  of  these 
kinds,  (birds  especially,  in  which  this  restrictive  effect  of 
expenditure  is  most  conspicuous),  the  connexion  between 
cessation  of  growth  and  commencement  of  reproduction,  is 
distinct.  But  we  also  saw  (§  46)  that  where,  as  in  the  Cro- 
codile and  the  Pike,  the  conditions  and  habits  of  life  are  such, 
that  expenditui*e  does  not  overtake  assimilation  as  the  size 
increases,  there  is  no  precise  limit  of  growth  ;  and  in  creatures 
thus  circumstanced,  we  may  naturally  look  for  a  compara- 
tively indeterminate  relation  between  declining  growth  and 
commencing  reproduction.*  There  is,  indeed,  among 

fishes,  at  least  one  case  which  appears  very  anomalous.  The 
male  parr,  or  young  of  the  male  salmon,  a  fish  of  four  or  five 
inches  in  length,  is  said  to  produce  milt.  Having,  at  this 
early  stage  of  its  growth,  not  one  hundredth  of  the  weight 
of  a  full-grown  salmon,  how  does  its  production  of  milt 
consist  with  the  alleged  general  law  ?  The  answer  must  be 
in  a  great  measure  hypothetical.  If  the  salmon  is  (as  it 
appears  in  its  young  state)  a  species  of  fresh-water  trout, 
that  has  contracted  the  habit  of  annually  migrating  to  the 
sea,  where  it  finds  a  food  on  which  it  thrives — if  the  original 
size  of  this  species  was  not  much  greater  than  that  of  the 
parr  (which  is  nearly  as  large  as  some  varieties  of  lake-trout 
and  river-trout) — and  if  the  limit  of  growth  in  the  trout 
tribe  is  very  indefinite,  as  we  know  it  to  be ;  then  we 
may  reasonably  infer,  that  the  parr  has  nearly  the  adult 
form  and  size  of  this  species  of  trout,  before  it  acquired 
its  migratory  habit ;   and  that  this  production  of  milt,  is, 

•  I  owe  to  Mr  Lubbock  an  important  confirmation  of  tbis  view.  After  stat- 
ing Lis  belief,  that  between  Crustaceans  and  Insects,  there  exists  a  physiological 
relation  analogous  to  that  which  exists  between  watcr-vertebrata  and  land-verte- 
brata;  he  pointed  out  to  me,  that  while  among  Insects,  there  is  a  definite  limit 
of  growth,  and  an  accompanying  definite  commencement  of  reproduction,  among 
Crustaceans,  where  growth  has  no  definite  limit,  there  is  no  definite  relation 
between  the  commencement  of  reproduction  and  the  decrease  or  arrest  of  growth 


232  THE    INDUCTIONS    OF    BIOLOGY. 

in  such,  case,  a  concomitant  of  the  incipient  decline  of 
growth  naturally  arising  in  the  species,  when  living  under 
the  conditions  of  its  remote  ancestors.  If  this  be  admitted, 
the  immense  subsequent  growth  of  the  parr  into  the  salmon, 
must  be  regarded  as  due  to  a  suddenly -increased  facility  in 
obtaining  food — a  facility  which  removes  to  a  great  distance 
the  limit  at  which  assimilation  is  balanced  by  expenditure  ; 
and  which  has  the  effect,  analogous  to  that  produced  in 
plants,  of  arresting  the  incipient  reproductive  process,  and 
causing  a  resumption  of  growth.  A  confirmation  of  this 
view  may  be  drawn  from  the  fact,  that  when  the  parr,  after 
its  first  migration  to  the  sea,  returns  to  fresh  water,  having 
increased  in  a  few  months  from  a  couple  of  ounces  to  five  or 
six  pounds,  it  no  longer  shows  any  fitness  for  propagation  : 
the  grilse,  or  immature  salmon,  does  not  produce  milt  or 
spawn.  But  without  citing  further  illustrations,  or 

attempting  to  meet  further  difficulties,  it  has,  I  think,  been 
made  sufficiently  clear,  that  some  such  connexion  as  that  al- 
leged, exists.  Traversed,  as  is  this  relation  between  commence- 
ment of  sexual  reproduction  and  declining  rate  of  growth,  by 
various  other  relations,  it  is  quite  as  manifest  as  we  can 
expect  it  to  be. 

The  general  law  to  which  both  homogenesis  and  hetero- 
genesis  conform,  thus  appears  to  be,  that  the  products  of  a 
fertilized  germ  go  on  accumulating  by  simple  growth,  so  long 
as  the  forces  whence  growth  results  are  greatly  in  excess  of 
the  antagonist  forces ;  but  that  when  diminution  of  the  one 
set  of  forces,  or  increase  of  the  other,  causes  a  considerable 
decline  in  this  excess,  and  an  approach  towards  equilibrium, 
fertilized  germs  are  again  produced.  Whether  the  germ- 
product  be  organized  round  one  axis,  or  round  the  many 
uxes  that  arise  by  agamogenesis — whether  the  development 
be  continuous  or  discontinuous  ;  matters  not.  "Whether,  as 
in  concrete  organisms  like  the  higher  animals,  this  approach 
to  equilibrium  results  from  that  disproportionate  increase  of 
expenditure  entailed  by  increase  of  size;  or  whether,  as  in 


GEXKSIS.  233 

partially  and  wholly  discrete  organisms,  like  most  plants  and 
many  inferior  animals,  this  approach  to  equilibrium  results 
from  absolute  or  relative  decline  of  nutrition  ;  matters  not. 
In  any  case,  the  recurrence  of  gamogenesis  is  associated  with 
u  more  or  less  marked  decrease  in  thte  excess  of  tissue-pro- 
ducing power.  We  cannot  say,  indeed,  that  a  do* 
ciease  in  this  excess  always  results  in  gamogenesis ;  for  wo 
have  evidence  to  the  contrary,  in  the  fact  that  some  organ- 
isms multiply  for  an  indefinite  period  by  agamogenesis  only. 
Thus,  the  weeping  willow,  which  has  been  propagated  through- 
out Europe,  does  not  seed  in  Europe ;  and  yet,  as  the  weep- 
ing willow,  by  its  large  size  and  the  multiplication  of 
generation  upon  generation  of  lateral  axes,  presents  the  same 
causes  of  local  innutrition  as  other  trees,  we  cannot  ascribe 
the  absence  of  sexual  axes  to  the  continued  predominance  of 
nutrition.  Among  animals,  too,  the  anomalous  case  of  the 
Tineidce,  a  group  of  moths  in  which  parthenogenetic  mul- 
tiplication goes  on- for  generation  after  generation,  shows  us 
that  gamogenesis  does  not  necessarily  result  from  an  approxi- 
mate balance  of  assimilation  by  expenditure.  What  we  must 
say,  is,  that  an  approach  towards  equilibrium  between  the 
forces  which  cause  growth  and  the  forces  which  oppose 
growth,  is  the  chief  condition  to  the  recurrence  of  gamo- 
genesis ;  but  that  there  are  other  unknown  conditions,  in  the 
absence  of  which  this  approach  to  equilibrium  is  not  followed 
by  gamogenesis. 

§  79.  The  above  induction  is  an  approximate  answer  to 
the  question — When  does  gamogenesis  recur  ?  but  not  to  the 
question  which  was  propounded —  Why  does  gamogenesis  re- 
cur?—  Why  cannot  multiplication  be  carried  on  in  all  cases, 
as  it  is  in  many  cases,  by  agamogenesis  ?  As  already  said, 
biologic  science  is  not  yet  advanced  enough  to  reply.  Mean- 
while, the  evidence  above  brought  together,  suggests  a  cer- 
tain hypothetical  answer,  which  it  may  be  well  to  set  down. 

Seeing  as  we  do,  on  the  one  hand,  that  gamogenesis  recuxa 
16 


234  THE    INDUCTIONS    OF    BIOLOGY. 

only  in  individuals  that  are  approaching  towards  a  state  of 
organic  equilibrium ;  and  seeing,  on  the  other  hand,  as  we 
do,  that  the  sperm-cells  and  germ-cells  thrown  off  by  such 
individuals,  are  cells  in  which  developmental  changes  have 
ended  in  quiescence,  but  in  which,  after  their  union,  there 
arises  a  process  of  active  cell- formation  ;  we  may  suspect 
that  the  approach  towards  a  state  of  general  equilibrium  in 
such  gamogenetic  indiviluals,  is  accompanied  by  an  approach 
towards  molecular  equilibrium  in  them ;  and  that  the  need 
for  this  union  of  sperm-cell  and  germ-cell,  is  the  need  for 
overthrowing  this  equilibrium,  and  re-establishing  active  mole- 
cular change  in  the  detached  germ — a  result  which  is  pro- 
bably effected  by  mixing  the  slightly  different  physiological 
units  of  slightly  different  individuals.  The  several  argu- 
ments that  may  be  brought  in  support  of  this  view,  cannot 
be  satisfactorily  set  forth  until  after  the  topics  of  Heredity 
and  Variation  have  been  dealt  with.  Leaving  it  for  the  pre- 
sent, I  propose  hereafter  to  reconsider  thfs  question,  in  con- 
nexion with  sundry  others  that  are  raised  by  the  phenomena 
of  Genesis. 

Before  ending  the  chapter,  however,  it  may  be  well  to  note 
the  relations  between  these  different  modes  of  multiplication, 
and  the  conditions  of  existence  under  which  they  are  respect- 
ively habitual.  While  the  explanation  of  the  teleologist  is 
untrue,  it  is  often  an  obverse  to  the  truth  ;  for  though,  on  the 
hypothesis  of  Evolution,  it  is  clear  that  things  are  not 
arranged  thus  or  thus  for  the  securing  of  special  ends,  it  is 
also  clear,  that  arrangements  which  do  secure  these  special 
ends,  tend  continually  to  establish  themselves — are  establish- 
ed by  their  fulfilment  of  these  ends.  Besides  insuring  a 
structural  fitness  between  each  kind  of  organism  and  its  cir- 
cumstances, the  working  of  "  natural  selection  "  also  insures 
a  fitness  between  the  mode  and  rate  of  multiplication  of  each 
kind  of  organism  and  its  circumstances.  We  may,  therefore, 
without  any  teleological  implication,  consider  the  fitness  of 


GENESIS.  236 

homogenesis  and  heterogenesis  to  the  needs  of  the  different 
classes  of  organisms  which  exhibit  them. 

One  of  the  facts  to  be  observed,  is,  that  heterogenesis  pre- 
vails among  organisms  of  which  the  food,  though  abundant 
compared  with  their  expenditure,  is  dispersed  in  such  a  way 
that  it  cannot  be  appropriated  in  a  wholesale  manner.  Pro- 
topliyta,  subsisting  on  diffused  gases  and  decaying  organic 
matter  in  a  state  of  minute  subdivision  ;  and  Protozoa,  to 
which  food  comes  in  the  shape  of  extremely  small  floating 
particles  ;  are  enabled  by  their  rapid  agamogenetic  multipli- 
cation, to  obtain  materials  for  growth,  better  than  they  would 
do  did  they  not  thus  continually  divide  and  disperse  in  pur- 
suit of  it.  The  higher  plants,  having  for  nutriment  the  car- 
bonic acid  of  the  air  and  certain  mineral  components  of  the 
soil,  show  us  modes  of  multiplication  adapted  to  the  fullest 
utilization  of  these  substances.  A  herb,  with  but  little  power 
of  forming  the  woody-fibre  requisite  to  make  a  stem  that  can 
support  wide-spreacling  branches,  after  producing  a  few  sex- 
less axes,  produces  sexual  ones  ;  and  maintains  its  race  better 
by  the  consequent  early  dispersion  of  seeds,  than  by  a  further 
production  of  sexless  axes.  But  a  tree,  able  to  lift  its  suc- 
cessive generations  of  sexless  axes  high  into  the  air,  where 
each  axis  gets  carbonic  acid  and  light  almost  as  freely  as  if  it 
grew  by  itself,  may  with  advantage  go  on  budding-out  sex- 
less axes  year  after  year;  since  it  thereby  increases  its  sub- 
sequent power  of  budding-out  sexual  axes.  Meanwhile,  it 
may  advantageously  transform  into  seed-bearers,  those  axes 
which,  in  consequence  of  their  less  direct  access  to  materials 
absorbed  by  the  roots,  are  failing  in  their  nutrition ;  for  in 
doing  this,  it  is  throwing-off  from  a  point  at  which  sus- 
tenance is  deficient,  a  migrating  group  of  germs  that  may 
find  sustenance  elsewhere.  The  heterogenesis  displayed  by 
animals  of  the  Coelenterate  type,  has  evidently  a  like  utility. 
A  polype,  feeding  on  minute  annelids  and  crustaceans,  which, 
flitting  through  the  water,  come  in  contact  with  its  tentacles,' 


236  THE    INDUCTIONS    OF    BIOLOGY. 

and  limited  to  that  quantity  of  prey  which  chance  brings 
within  its  grasp ;  buds  out  young  polypes  which,  either  as  a 
colony  or  as  dispersed  individuals,  spread  their  tentacles 
through  a  larger  space  of  water  than  the  parent  alone  can ; 
and  by  producing  them,  the  parent  better  insures  the  continu- 
ance of  its  species,  than  it  would  do  if  it  went  on  slowly  grow- 
ing until  its  nutrition  was  nearly  balanced  by  its  waste,  and 
then  multiplied  by  gamogenesis.  Similarly  with  the  Aphis. 
Living  on  sap  sucked  through  its  proboscis  from  tender  shoots 
and  leaves,  and  able  thus  to  take  in  but  a  very  small  quan- 
tity in  a  given  time,  this  creature's  race  is  more  likely  to 
be  preserved  by  a  rapid  asexual  propagation  of  small  indi- 
viduals, which  disperse  themselves  over  a  wide  but  nowhere 
rich  area  of  nutrition,  than  it  would  be  did  the  individual 
growth  continue  so  as  to  produce  large  individuals  multiply- 
ing sexually.  While  at  the  same  time  we  see,  that  when 
autumnal  cold  and  diminishing  supply  of  sap,  put  a  check  to 
growth,  the  recurrence  of  gamogenesis,  and  production  of 
fertilized  ova  that  remain  dormant  through  the  winter,  is 
more  favourable  to  the  preservation  of  the  race,  than  would  be 
a  further  continuance  of  agamogenesis.  On  the 

other  hand,  it  is  obvious  that  among  the  higher  animals, 
living  on  food  which,  though  dispersed,  is  more  or  less 
aggregated  into  large  masses,  this  alternation  of  gamic  and 
agamic  reproduction  ceases  to  be  useful.  The  development 
of  the  germ- product  into  a  single  organism  of  considerable 
bulk,  is  in  many  cases  a  condition  without  which  these  large 
masses  of  nutriment  could  not  be  appropriated ;  and  here  thu 
formation  of  many  individuals  instead  of  one,  would  be  fatal. 
But  we  still  see  the  beneficial  results  of  the  general  law — the 
postponement  of  gamogenesis  until  the  rate  of  growth  begins 
to  decline.  For  so  long  as  the  rate  of  growth  continues 
rapid,  it  is  a  proof  that  the  organism  gets  food  with  great 
facility — that  expenditure  is  not  such  as  seriously  to  check 
accumulation  ;  and  that  the  size  reached  is  as  yet  not  disad- 
vantageous— or  rather,  indeed,  that  it  is  advantageous.    But 


GENESIS.  l2'Sl 

when  the  rate  of  growth  is  much  decreased  by  the  compara- 
tively rapid  increase  of  expenditure — when  the  excess  of 
assimilative  power  is  diminishing  in  such  a  way  as  to  indi- 
cate its  approaching  disappearance ;  it  becomes  needful  for 
the  maintenance  of  the  species,  that  this  excess  shall  be 
turned  to  the  production  of  new  individuals  ;  since,  did 
growth  continue  until  this  excess  disappeared  through  the 
complete  balancing  of  assimilation  and  expenditura,  the  pro- 
duction of  new  individuals  would  be  either  impossible  or  fatal 
to  the  parent.  And  it  is  clear  that  "  natural  selection  "  will 
continually  tend  to  determine  the  period  at  which  gamo- 
genesis  commences,  in  such  a  way  as  most  favours  the  main- 
tenance of  the  race. 

Here,  too,  may  fitly  be  pointed  out  the  fact,  that,  by 
"natural  selection,"  there  will  in  every  case  be  produced,  the 
most  advantageous  proportion  of  males  and  females.  If  the 
conditions  of  life  are  such  as  to  render  a  greater  or  less  in- 
equality of  the  sexes  beneficial  to  the  species,  in  respect 
either  of  the  number  of  the  offspring,  or  the  character  of  the 
offspring ;  then,  those  varieties  of  the  species  which,  from  any 
cause,  approach  more  than  other  varieties  towards  thL 
beneficial  degree  of  inequality,  will  be  apt  to  supplant  other 
varieties.  And  conversely,  where  equality  in  the  number  of 
males  and  females  is  beneficial,  the  equilibrium  will  be  main- 
tained by  the  dying  out  of  such  varieties  as  produce  offspring 
among  which  the  sexes  are  not  balanced. 


CHAPTER  VIII. 

HEREDITY. 

{$  80.  Already,  in  the  last  two  chapters,  the  law  of  heredi- 
tary transmission  has  been  tacitly  assumed ;  as,  indeed,  it 
unavoidably  is  in  all  such  discussions.  Understood  in  its 
entirety,  the  law  is,  that  each  plant  or  animal  produces 
others  of  like  kind  with  itself:  the  likeness  of  kind  consist- 
ing, not  so  much  in  the  repetition  of  individual  traits,  as  in 
the  assumption  of  the  same  general  structure.  This  truth  has 
been  rendered  so  familiar  by  daily  illustration,  as  almost  to 
have  lost  its  significance.  That  wheat  produces  wheat — that 
existing  oxen  have  descended  from  ancestral  oxen — that  every 
unfolding  organism  eventually  takes  the  form  of  the  class, 
order,  />enus,  and  species  from  which  it  sprang ;  is  a  fact 
which,  by  force  of  repetition,  has  acquired  in  our  minds 
almost  the  aspect  of  a  necessity.  It  is  in  this,  however, 
that  Heredity  is  principally  displayed :  the  phenomena  com- 
monly referred  to  it,  being  quite  subordinate  manifestations. 
And,  as  thus  understood,  Heredity  is  universal.  The  various 
instances  of  heterogenesis  lately  contemplated,  seem,  indeed, 
to  be  at  variance  with  this  assertion.  But  they  are  not 
really  so.  Though  the  recurrence  of  like  forms,  is,  in  these  in- 
stances, not  direct  but  cyclical,  still,  the  like  forms  do  recur ; 
and  when  taken  together,  the  group  of  forms  produced  during 
one  of  the  cycles,  is  as  much  like  the  groups  produced  in  pre- 
ceding cycles,  as  the  single  individual  arising  by  homo- 
genesis,  is  like  ancestral  individuals. 


HEREDITY.  239 

"While,  however,  the  general  truth  that  organisms  of  a 
given  type  uniformly  descend  from  organisms  of  the  same 
type,  is  so  well  established  by  infinite  illustrations,  as  to  have 
assumed  the  character  of  an  axiom ;  it  is  not  universally 
admitted  that  non-typical  peculiarities  are  inherited.  While 
the  botanist  would  be  so  incredulous  if  told  that  a  plant  oi 
one  class  had  produced  a  plant  of  another  class,  or  that  from 
seeds  belonging  to  one  order- individuals  belonging  to  another 
order  had  grown,  that  he  would  deem  it  needless  to  examine 
the  evidence ;  and  while  the  zoologist  would  treat  with  con- 
tempt the  assertion,  that  from  the  egg  of  a  fish  a  reptile  had 
arisen,  or  that  an  implacental  mammal  had  borne  a  pla- 
cental mammal,  or  that  an  unguiculate  quadruped  had  sprung 
from  an  ungulate  quadruped,  or  even  that  from  individuals 
of  one  species  offspring  of  an  allied  species  had  proceeded ; 
yet  there  are  botanists  and  zoologists  who  do  not  consider  it 
certain,  that  the  minor  specialities  of  organization  are  trans- 
mitted from  one  generation  to  another.  Some  naturalists 
seem  to  entertain  a  vague  belief,  that  the  law  of  Heredity 
applies  only  to  main  characters  of  structure,  and  not  to  de- 
tails ;  or,  at  any  rate,  that  though  it  applies  to  such  details 
as  i  onstitute  differences  of  species,  it  does  not  apply  to 
smaller  details.  The  circumstance  that  the  tendency  to  re- 
petition, is  in  a  slight  degree  qualified  by  the  tendency  to 
variation  (which,  as  we  shall  hereafter  see,  is  but  an  indirect 
result  of  the  tendency  to  repetition),  leads  some  to  doubt, 
whether  Heredity  is  unlimited.  A  careful  weighing  of  the 
evidence,  however,  and  a  due  allowance  for  the  influences  by 
which  the  minuter  manifestations  of  Heredity  are  obscured 
will  remove  the  grounds  for  this  scepticism. 

First  in  order  of  importance,  comes  the  fact,  that  not  only 
are  there' uniformly  transmitted  from  an  organism  to  its 
offspring,  those  traits  of  structure  which  distinguish  the  class, 
order,  genus,  and  species ;  but  also  those  which  distinguish 
the  variety.  We  have  numerous  cases,  among  both  plants 
and  animals,  where,  b}-  natural  or  artificial  conditions,  there 


240  THE    INDUCTIONS   OF    BIOLOGY. 

have  been  produced  divergent  modifications  of  the  same 
species ;  and  abundant  proof  exists  that  the  members  of  any 
one  sub-species,  habitually  transmit  their  distinctive  pecu- 
liarities to  their  descendants.  Agriculturists  and 
gardeners  can  furnish  unquestionable  illustrations.  Several 
varieties  of  wheat  are  known  ;  of  which  each  reproduces 
itself.  Since  its  introduction  into  England,  there  have  been 
formed  from  the  potato,  a  number  of  sub-species:  some  of  them 
differing  greatly  in  their  forms,  sizes,  qualities,  and  periods 
of  ripening.  Of  peas,  also,  the  like  may  be  said.  And  the 
case  of  the  cabbage-tribe,  is  often  cited  as  showing  the  per- 
manent establishment  of  races  that  have  diverged  widely 
from  a  common  stock.  Among  fruits  and  flowers,  the  multi- 
plication of  kinds,  and  the  continuance  of  each  kind  with 
certainty  by  agamogenesis,  and  to  some  extent  by  gamo- 
genesis,  might  be  exemplified  without  end.  From  all 
sides  evidence  may  be  gathered  showing  a  like  persistence  of 
varieties  in  each  species  of  animal.  We  have  our  distinct 
breeds  of  sheep,  our  distinct  breeds  of  cattle,  our  distinct 
breeds  of  horses  :  each  breed  maintaining  its  characteristics. 
The  several  sorts  of  dogs,  which,  if  we  accept  the  physiolo 
gical  test,  we  must  consider  as  all  of  one  species,  show  us  in 
a  marked  manner  the  hereditary  transmission  of  small  differ- 
ences— each  sort,  when  kept  pure,  reproducing  itself  not 
only  in  size,  form,  colour,  and  quality  of  hair,  but  also  in 
disposition  and  speciality  of  intelligence.  Rabbits,  too,  have 
their  permanently-established  races.  And  in  the  Isle  of  Man, 
we  have  a  tail-less  kind  of  cat.  Even*  in  the  absence 
of  other  evidence,  that  which  ethnology  furnishes  would 
suffice.  Grant  them  to  be  derived  from  one  stock,  and  the 
varieties  of  man  yield  proof  upon  proof  that  non-specific 
traits  of  structure  are  bequeathed  from  generation  to  gener- 
ation. Or  grant  only  that  there  is  evidence  of  their  deriva- 
tion from  several  stocks,  and  we  still  have,  between  races  de- 
scended from  a  common  stock,  distinctions  which  prove  the 
inheritance    of    minor    peculiarities.      Besides   seeing   that 


HEREDITY.  24:1 

negroes  continue  to  produce  negroes,  copper-coloured  men  to 
produce  men  of  a  copper  colour,  and  the  fair-skinned  races 
to  perpetuate  their  fair  skins — besides  seeing  that  the  broad- 
faced  and  flat-nosed  Calmuck  begets  children  with  broad  faces 
and  flat  noses,  while  the  Jew  bequeaths  to  his  offspring  the 
features  which  have  so  long  characterized  Jews  ;  we  see  that 
those  small  unlikenesses  which  distinguish  more  nearly-allied 
varieties  of  men,  are  maintained  from  generation  to  generation. 
In  Germany,  the  ordinary  shape  of  skull  is  appreciably  differ- 
ent from  that  common  in  Britain :  near  akin  though  the 
Germans  are  to  the  British.  The  average  Italian  face  con- 
tinues to  be  unlike  the  faces  of  northern  nations.  The  French 
character  is  now,  as  it  was  centuries  ago,  contrasted  in  sundry 
respects  with  the  characters  of  neighbouring  peoples.  Nay, 
even  between  races  so  closely  allied  as  the  Scotch  Celts,  the 
Welch  Celts,  and  the  Irish  Celts,  appreciable  differences  of 
form  and  nature  have  become  established. 

That  sub-species  and  sub-sub-species,  thus  exemplify  that 
same  general  law  of  inheritance  which  shows  itself  in  the  per- 
petuation of  ordinal,  generic,  and  specific  peculiarities ;  is 
strong  reason  for  the  belief  that  this  general  law  is  unlimited 
in  its  application.  In  addition  to  the  warrant  which  this  be- 
lief derives  from  evidence  of  this  kind,  it  has  also  the  support 
of  still  more  special  evidence.  Numerous  illustrations  of  He- 
redity are  yielded  by  experiment,  and  by  direct  observation  of 
successive  generations.  They  are  divisible  into  two  classes. 
In  the  one  class  come  cases  where  congenital  peculiarities, 
not  traceable  to  any  obvious  causes,  are  bequeathed  to  de- 
scendants. In  the  other  class  come  cases  where  the  peculiar- 
ities thus  bequeathed  are  not  congenital,  but  have  resulted 
from  changes  of  functions  during  the  lives  of  the  individuals 
bequeathing  them.  "We  will  consider  first  the  cases  that 
come  in  the  first  class. 

§  81.  Note  at  the  outset  the  character  of  the  chief  testi- 
mony.    Excluding  those  inductions  that  have  been  so  fully 


242  THE    INDUCTIONS   OF    BIOLOGY. 

verified  as  to  rank  with  exact  science,  there  are  no  inductions 
so  trustworthy  as  those  which  have  undergone  the  mercantile 
test.  When  we  have  thousands  of  men  whose  profit  or  loss 
depends  on  the  truth  of  the  inferences  they  draw  from  simple 
and  perpetualty- repeated  observations  ;  and  when  we  find 
that  the  inference  arrived  at,  and  handed  down  from  genera- 
tion to  generation  of  these  deeply-interested  observers,  has 
become  an  unshakable  conviction  ;  we  may  accept  it  without 
hesitation.  In  breeders  of  animals  we  have  such  a  class,  led 
by  such  experiences,  and  entertaining  such  a  conviction — the 
conviction  that  minor  peculiarities  of  organization  are  in- 
herited as  well  as  major  peculiarities.  Hence  the  immense 
prices  given  for  successful  racers,  bulls  of  superior  forms, 
sheep  that  have  certain  desired  peculiarities.  Hence  the 
careful  record  of  pedigrees  of  high-bred  horses  and  sporting 
dogs.  Hence  the  care  taken  to  avoid  intermixture  with  in- 
ferior stocks.  Citing  the  highest  authorities  respecting  the 
effects  of  breeding  from  animals  having  certain  superiorities, 
with  the  view  of  propagating  those  superiorities,  Mr  Darwin 
writes  : — "  Youatt,  who  was  probably  better  acquainted  with 
the  works  of  agriculturists  than  almost  any  other  individual, 
and  who  was  himself  a  very  good  judge  of  an  animal,  speaks 
of  the  principle  of  selection  as  '  that  which  enables  the  agri- 
culturist not  only  to  modify  the  character  of  his  flock,  but  to 
change  it  altogether.  It  is  the  magician's  wand,  by  means  of 
which  he  may  summon  into  life  whatever  form  and  mould  he 
pleases.'  "  Lord  Somerville,  speaking  of  what  breeders  have 
done  for  sheep,  says  : — "  It  would  seem  that  they  had  chalked 
upon  a  wall  a  form  perfect  in  itself  and  then  given  it  exist- 
en  oe."  That  most  skilful  breeder,  Sir  John  Sebright,  used  to 
say,  with  respect  to  pigeons,  that  "he  would  produce  any 
given  feather  in  three  years,  but  it  would  take  him  six  years 
to  obtain  head  and  beak."  In  all  which  statements  the 
tacit  assertion  is,  that  individual  traits  are  bequeathed 
from  generation  to  generation ;  and  that  when  they  are 
not  brought  into  conflict  with  opposite  traits,  they  may  be 


HEREDITY.  243 

so  perpetuated  and  increased  as  to  become  permanent  dis- 
tinctions. 

Of  special  instances,  there  are  many  besides  that  of  the  oft 
en -cited  Otter-breed  of  sheep,  descended  from  a  single  short 
legged  lamb,  and  that  of  the  six-fingered  Gratio  Kelleia,  who 
transmitted  his  peculiarity  in  different  degrees,  to  several  of 
his  children  and  to  some  of  his  grandchildren.  In  a  paper  con. 
tributed  to  the  Edinburgh  New  Philosophical  Journal  for  July 
1863,  Dr  Struthers  gives  several  cases  of  hereditary  digital 
variations.  Esther  P — ,  who  had  six  fingers  on  one  hand,  be- 
queathed this  malformation,  along  some  lines  of  her  descend- 
ants, fcr  two,  three,  and  four  generations.  A —  S —  inherited 
an  exha  digit  on  each  hand  and  each  foot  from  his  father; 
and  C —  G — ,  who  also  had  six  fingers  and  six  toes, had  an  aunt 
and  a  grandmother  similarly  formed.  A  collection  of  evidence 
has  been  made  by  Mr  Sedgwick,  and  published  by  him  in  the 
Medico- Chirurgical  Review  for  April  and  for  July  1863,  in 
two  articles  on  "  The  Influence  of  Sex  in  limiting  Hereditary 
Transmission."  From  these  articles  are  selected  the  following 
cases  and  authorities  : — Augustin  Duforet,  a  pastry-cook  of 
Douai,  who  had  but  two  instead  of  three  phalanges  to  all  his 
fingers  and  toes,  inherited  this  malformation  from  his  grand- 
father and  father,  and  had  it  in  common  with  an  uncle  and 
numerous  cousins.  An  account  has  been  given  by  Dr  Lepine, 
of  a  man  with  only  three  fingers  on  each  hand  and  four  toes 
on  each  foot,  and  whose  grandfather  and  son  exhibited  the 
like  anomaly.  Bechet  describes  Victoire  Barre  as  a  woman 
who,  like  her  father  and  sister,  had  but  one  developed  finger 
on  each  hand,  and  but  two  toes  on  each  foot,  and  whose  mon- 
strosity re-appeared  in  two  daughters.  And  there  is  a  case 
where  the  absence  of  two  distal  phalanges  on  the  hands  was 
traced  for  two  generations.  The  various  recorded  instances 
in  which  there  has  been  transmission  from  one  generation  to 
another,  of  webbed-fingers,  of  webbed-toes,  of  hare-lip,  of 
congenital  luxation  of  the  thigh,  of  absent  patella?,  of 
club-foot,  &c,  would  occupy  more  space  than  can  here  bo 


24:4:  THE    INDUCTIONS    OF   BIOLOGY. 

spared.  Defects  in  the  organs  of  sense  are  also  not 

un frequently  inherited.  Four  sisters,  their  mother,  and 
grandmother,  are  described  by  Duval  as  similarly  affected  by 
cataract.  Prosper  Lucas  details  an  example  of  hereditary  am- 
aurosis affecting  the  females  of  a  family  for  three  generations. 
Duval,  Graffe,  Dufon,  and  others  testify  to  like  cases  coming 
under  their  observation.*  Deafness,  too,  is  occasionally  trans- 
mitted from  parent  to  child.  There  are  deaf-mutes  whose 
imperfections  have  been  derived  from  ancestors;  and  mal- 
formations of  the  external  ears  have  also  been  perpetuated  in 
offspring.  Of  transmitted  peculiarities  of  the  skin 

and  its  appendages,  many  illustrations  have  been  noted.  One 
is  that  of  a  family  remarkable  for  enormous  black  eyebrows  ; 
another  that  of  a  family  in  which  every  member  had  a  lock  of 
hair  of  a  lighter  colour  than  the  rest  on  the  top  of  the  head ; 
and  there  are  also  instances  of  congenital  baldness  being 
hereditary.  Entire  absence  of  teeth,  absence  of  particular, 
teeth,  and  anomalous  arrangements  of  teeth,  are  recorded  as 
traits  that  have  descended  to  children.  And  we  have  evidence 
that  soundness  and  unsoundness  of  teeth  are  transmissible. 

The  inheritance  of  such  diseases  as  gout,  consumption,  and 
insanity,  is  universally  admitted.  Among  the  less-common 
diseases  of  which  the  descent  from  one  generation  to  another 
has  been  observed,  are,  ichthyosis,  leprosy,  pityriasis,  sebace- 
ous tumours,  plica  polonica,  dipsomania,  somnambulism,  cata- 
lepsy, epilepsy,  asthma,  apoplexy,  elephantiasis.  General 
nervousness  displayed  by  parents,  almost  always  re-appears 
in  their  children.  Even  a  bias  towards  suicide  appears  to 
be  sometimes  hereditary. 

§  82.  To  prove  the  transmission  of  those  structural  pecu- 
liarities that  have  resulted  from  functional  peculiarities,  is, 

*  While  this  chapter  is  passing  through  the  press,  I  learn  from  Mr.  White 
Cooper,  that  not  only  are  near  sight,  long  sight,  dull  sight,  and  squinting, 
hereditary  ;  but  that  a  peculiarity  of  vision  confined  to  one  eye,  is  frequently 
transmitted — re-appearing  in  the  same  eye  in  offspring. 


TIER  EDITY. 


245 


for  several  reasons,  comparatively  difficult.  Changes  pro- 
duced in  the  sizes  of  parts  by  changes  in  their  amounts  of 
action,  are  mostly  unobtrusive.  A  muscle  that  has  increased 
in  bulk,  is  so  obscured  by  natural  or  artificial  clothing,  that  un- 
less the  alteration  is  extreme  it  passes  without  remark.  Such 
nervous  developments  as  are  possible  in  the  course  of  a  single 
life,  cannot  be  seen  externally.  Visceral  modifications  of  a 
normal  kind,  are  observable  but  obscurely,  or  not  at  all.  And 
if  the  changes  of  structure  worked  in  individuals  by  changes 
in  their  habits,  are  thus  difficult  to  trace ;  still  more  difficult 
to  trace  must  be  the  transmission  of  them — further  hidden, 
as  this  is,  by  the  influence  of  other  individuals  that  are  often 
otherwise  modified  by  other  habits.  Moreover,  such  special- 
ities of  structure  as  are  due  to  specialities  of  function,  are 
usually  entangled  with  specialities  of  structure  that  are,  or 
may  be,  due  to  selection,  natural  or  artificial.  In  the  majority 
of  cases,  it  is  impossible  to  say  that  a  structural  peculiarity 
which  seems  to  have  arisen  in  offspring  from  a  functional 
peculiarity  in  the  parent,  is  wholly  independent  of  some 
congenital  peculiarity  of  structure  in  the  parent,  which  in- 
duced this  functional  peculiarity.  We  are  restricted  to 
cases  with  which  natural  or  artificial  selection  can  have  had 
nothing  to  do  ;  and  such  cases  are  difficult  to  find.  Some, 
however,  may  here  be  noted. 

A  species  of  plant  that  has  been  transferred  from  one  soil 
or  climate  to  another,  frequently  undergoes  what  botanists 
call  "  a  change  of  habit " — a  change  which,  without  affecting 
its  specific  characters,  is  yet  conspicuous.  In  its  new  locality, 
the  species  is  distinguished  by  leaves  that  are  much  larger, 
or  much  smaller,  or  differently  shaped,  or  more  fleshy  ;  or 
instead  of  being,  as  before,  comparatively  smooth,  it  becomes 
hairy;  or  its  stem  becomes  woody  instead  of  being  herbaceous; 
or  its  branches,  no  longer  growing  upwards,  assume  a  droop- 
ing character.  Now  these  "  changes  of  habit"  are  clearly  de- 
termined by  functional  changes.  Occurring,  as  they  do,  in 
many  individuals  that  have  undergone  the  same  transportation, 


246 


THE    INDUCTIONS    OF  BIOLOGY. 


they  cannot  be  classed  as  "  spontaneous  variations."  They 
are  modifications  of  structure,  consequent  on  modifications  of 
function,  that  have  been  produced  by  modifications  in  the 
actions  of  external  forces.  And  as  these  modifications  re-ap- 
pear in  succeeding  generations,  we  have,  in  them,  examples 
of  functionally-established  variations  that  are  hereditarily 
transmitted.  Further  evidence  is  supplied  by  what 

are  called  "  sports  "  in  plants.  These  are  of  two  kinds — the 
gamogenetic  and  the  agamogenetic.  The  gamogenetic  may 
be  ascribed  wholly  to  "  spontaneous  variations ;"  or  if  they  are 
partly  due  to  the  inheritance  of  structural  changes  that  are 
produced  by  functional  changes,  this  cannot  be  proved.  But 
where  the  individuals  displaying  the  variations  arise  by 
agamogenesi3,  the  reverse  is  the  case :  spontaneous  variation 
is  out  of  the  question ;  and  the  only  possible  interpretation  is 
deviation  of  structure  caused  by  deviation  of  function.  A 
new  axis  which  buds  out  from  a  parent-axis,  assumes  an  un- 
like character — gives  off  lobed  leaves  in  place  of  single  leaves, 
or  has  an  otherwise  different  mode  of  growth.  This  change 
of  structure  implies  change  in  the  developmental  actions 
which  produced  the  new  bud — change,  that  is,  in  the  actions 
going  on  in  the  parent  shoot  —  functional  change.  And 
since  the  modified  structure  thus  impressed  on  the  new  shoot 
by  modified  function,  is  transmitted  by  it  to  all  the  shoots 
it  bears  ;  we  are  obliged  to  regard  the  case  as  one  of  acquired 
modification  that  has  become  hereditary. 

Evidence  of  analogous  changes  in  animals,  is  difficult  to 
disentangle.  Only  among  domesticated  animals,  have  we  any 
opportunity  of  tracing  the  effects  of  altered  habits  ;  and  here, 
in  nearly  all  cases,  artificial  selection  has  obscured  the  results. 
Still,  there  are  some  facts  which  seem  to  the  point.  Mr 
Darwin,  while  ascribing  almost  wholly  to  "  natural  selection  " 
the  production  of  those  modifications  which  eventuate  in 
differences  of  species,  nevertheless  admits  the  effects  of  use  and 
disuse.  He  says — "  I  find  in  the  domestic  duck  that  the  bones 
of  the  wing  weigh  less  and  the  bones  of  the  leg  more,  in  pro- 


HEREDITY.  247 

portion  to  the  whole  skeleton,  than  do  the  same  hones  in  the 
wild  duck ;  and  I  presume  that  this  change  may  be  safely 
attributed  to  the  domestic  duck  flying  much  less,  and  walking 
more,  than  its  wild  parent.    The  great  and  inherited  develop- 
ment of  the  udders  in  cows  and  goats  in  countries  where  they 
are  habitually  milked,  in  comparison  with  the  state  of  these 
or  grans  in  other  countries,  is  another  instance  of  the  effect  of 
use.     Not  a  single  domestic  animal  can  be  named  which  has 
not  in  some  country  drooping  ears ;  and  the  view  suggested  by 
some  authors,  that  the  drooping  is  due  to  the  disuse  of  the 
muscles  of  the  ear,  from  the  animals  not  being  much  alarmed 
by  danger,  seems  probable."   Again — "  The  eyes  of  moles  and 
of  some  burrowing  rodents  are  rudimentary  in  size,  and  in 
some  cases  are  quite  covered  up  by  skin  and  fur.     This  state 
of  the  eyes  is  probably  due  to  gradual  reduction  from  disuse, 
but  aided  perhaps  by  natural  selection."  *     *     *  "  It  is  well 
known  that  several  animals,  belonging  to  the  most  differ- 
ent classes,  which  inhabit  the  caves  of  Styria  and  of  Kentucky, 
are  blind.      In  some  of  the  crabs  the  footstalk  of  the  eye  re- 
mains, though  the  eye  is  gone  ;  the  stand  for  the  telescope  is 
there,  though  the  telescope  with  its  glasses  has  been  lost.    As 
it  is  difficult  to  imagine  that  eyes,  though  useless,  could  be  in 
any  way  injurious  to  animals  living  in  darkness,  I  attribute 
their  loss  wholly  to  disuse."   The  direct  inheritance  of  an  ac- 
quired peculiarity  is  sometimes  observable.     Mr  Lewes  gives 
a  case.    He  "  had  a  puppy  taken  from  its  mother  at  six  weeks 
old,  who,  although  never  taught,  'to  beg'  (an  accomplishment 
his  mother  had  been  taught),  spontaneously  took  to  begging 
for  everything  he  wanted  when  about  seven  or  eight  months 
old  :  he  would  beg  for  food,  beg  to  be  let  out  of  the  room, 
nnd  one  day  was  found  opposite  a  rabbit  hutch  begging  for 
rabbits."  Instances  are  on  record,  too,  of  sporting  dogs  which 
spontaneously  adopted  in  the  field,  certain  modes  of  behaviour 
which  their  parents  had  learnt. 

But  the  best  examples  of  inherited  modifications  produced 
by  modifications  of  function,  occur  in  the  human  race.    To  no 


248  THE    INDUCTIONS   OF    BIOLOGY. 

other  cause  can  be  ascribed  the  rapid  metamorphoses  under- 
gone by  the  British  races  when  placed  in  new  conditions.  It 
is  notorious  that,  in  the  United  States,  the  descendants  of  the 
immigrant  Irish  lose  their  Celtic  aspect,  and  become  Ameri- 
canized. This  cannot  be  ascribed  to  intermarriage  with 
Americans ;  since  the  feeling  with  which  Irish  are  regard- 
ed by  Americans,  prevents  any  considerable  amount  of  inter- 
marriage. Equally  marked  is  the  case  of  the  immigrant 
Germans,  who,  though  they  keep  themselves  very  much 
apart,  rapidly  assume  the  prevailing  type.  To  say  that 
"  spontaneous  variation  "  increased  by  natural  selection,  can 
have  produced  this  effect,  is  going  too  far.  Races  so  numer- 
ous, cannot  have  been  supplanted  in  the  course  of  two  or 
three  generations  by  varieties  springing  from  them.  Hence 
there  is  no  escape  from  the  conclusion,  that  physical  and  so- 
cial conditions  have  here  wrought  modifications  of  function 
and  structure,  which  offspring  have  inherited  and  increased. 
Similarly  with  special  cases.  In  the  Cyclopaedia  of  Practical 
Medicine,  Yol.  II.  p.  419,  Dr  Brown  states  that  he  "has  in 
many  instances  observed  in  the  case  of  individuals  whose 
complexion  and  general  appearance  has  been  modified  by  re- 
sidence in  hot  climates,  that  children  born  to  them  subse- 
quently to  such  residence,  have  resembled  them  rather  in 
their  acquired  than  primaiy  mien." 

Some  special  modifications  of  organs  caused  by  special 
changes  in  their  functions,  may  also  be  noted.  That  large 
hands  are  inherited  by  men  and  women  whose  ancestors 
led  laborious  lives  ;  and  that  men  and  women  whose  descent, 
for  many  generations,  has  been  from  those  unused  to  manual 
labour,  commonly  have  small  hands  ;  are  established  opinions. 
It  seems  very  unlikely  that  in  the  absence  of  any  such  con- 
nexion, the  size  of  the  hand  should  thus  have  come  to  be 
generally  regarded  as  some  index  of  extraction.  That  there 
exists  a  like  relation  between  habitual  use  of  the  feet  and  large- 
ness of  the  feet,  we  have  strong  evidence  in  the  customs  of  the 
Chinese.     The  torturing  practice  of  artificially  arresting  the 


HEREDITY.  249 

growth  of  the  feet,  could  never  have  become  established  among 
the  ladies  of  China,  had  they  not  found  abundant  proof 
that  a  small  foot  was  significant  of  superior  rank — that  is 
of  a  luxurious  life — that  is  of  a  life  without  bodily 
labour.  There  is  some  evidence,  too,  that  modifica« 

tions  of  the  eyes,  caused  by  particular  uses  of  the  eyes,  are 
inherited.  Short  sight  appears  to  be  uncommon  in  rural 
populations  ;  but  it  is  frequent  among  classes  of  people  who 
use  their  eyes  much  for  reading  and  writing  ;  and  in  these 
classes,  short  sight  is  often  congenital.  Still  more  marked  is 
this  relation  in  Germany.  There,  the  educated  classes  are  no- 
toriously studious  ;  and  judging  from  the  numbers  of  young 
Germans  who  wear  spectacles,  there  is  reason  to  think  that 
congenital  myopia  is  very  frequent  among  them. 

Some  of  the  best  illustrations  of  functional  heredity,  are 
furnished  by  the  mental  characteristics  of  human  races.  Cer- 
tain powers  which  mankind  have  gained  in  the  course  of  civil- 
ization, cannot,  I  think,  be  accounted  for,  without  admitting 
the  inheritance  of  acquired  modifications.  The  musical  faculty 
is  one  of  these.  To  say  that  "  natural  selection"  has  developed 
it,  by  preserving  the  most  musically  endowed,  seems  an  in- 
adequate explanation.  Even  now  that  the  development  and 
prevalence  of  the  faculty  have  made  music  an  occupation  by 
which  the  most  musical  can  get  sustenance  and  bring  up 
families ;  it  is  very  questionable  whether,  taking  the  musical 
life  as  a  whole,  it  has  any  advantage  over  others  in  the 
struggle  for  existence  and  multiplication.  Still  more  if  we 
look  back  to  those  eaidy  stages  through  which  the  faculty  must 
have  passed,  before  definite  perception  of  melody  was  arrived 
at,  we  fail  to  see  how  those  possessing  the  rudimental  faculty 
in  a  somewhat  greater  degree  than  the  rest,  woftld  thereby  be 
enabled  the  better  to  maintain  themselves  and  their  children. 
If  so,  there  is  no  explanation  but  that  the  habitual  association 
of  certain  cadences  of  human  speech  with  certain  emotions, 
has  slowly  established  in  the  race  an  organized  and  inherited 
oonnexion  between  such  cadences  and  such  emotions ;  that  tho 
17 


250  THE   INDUCTIONS   OF   BIOLOGY. 

combination  of  such  cadences,  more  or  less  idealized,  which 
constitutes  melody,  has  all  along  had  a  meaning  in  the  average 
mind,  only  because  of  the  meaning  which  cadences  had  acquired 
in  the  average  mind  ;  and  that  by  the  continual  hearing  and 
practice  of  melody,  there  has  been  gained  and  transmitted  an 
increasing  musical  sensibility.  Confirmation  of  this 

view  may  be  drawn  from  individual  cases.  Grant  that  among 
a  people  endowed  with  musical  faculty  to  a  certain  degree, 
spontaneous  variation  will  occasionally  produce  men  possessing 
it  in  a  higher  degree  ;  it  cannot  be  granted  that  spontaneous 
variation  accounts  for  the  frequent  production,  by  such  highly- 
endowed  men,  of  men  still  more  highly  endowed.  On  the 
average,  the  offspring  of  marriage  with  others  not  similarly 
endowed,  will  be  less  distinguished  rather  than  more  distin- 
guished. The  most  that  can  be  expected  is,  that  this  unusual 
amount  of  faculty  shall  re-appear  in  the  next  generation  undi- 
minished. How  then  shall  we  explain  cases  like  those  of  Bach, 
Mozart,  and  Beethoven,  who  were  all  sons  of  men  having  un- 
usual musical  powers,  but  who  greatly  excelled  their  fathers 
in  their  musical  powers  ?  What  shall  we  say  to  the  facts, 
that  Haydn  was  the  son  of  the  organist,  that  Hummel  was 
born  to  a  music  master,  and  that  Weber's  father  was  a  dis- 
tinguished violinist?  .The  occurrence  of  so  many  cases  in 
one  nation,  within  a  short  period  of  time,  cannot  rationally 
be  ascribed  to  the  coincidence  of  "  spontaneous  variations."  It 
can  be  ascribed  to  nothing  but  inherited  developments  of 
structure,  caused  by  augmentations  of  function. 

But  the  clearest  proof  that  structural  alterations  caused  by 
alterations  of  function,  are  inherited,  occurs  when  the  alter- 
ations are  morbid.  "  Certain  modes  of  living  engender  gout ; " 
and  gout  is  transmissible.  It  is  well  known  that  in  persons  pre- 
viously healthy,  consumption  may  be  produced  by  unfavourable 
conditions  of  life — by  bad  and  insufficient  food  ;  by  foul,  damp, 
unventilated  habitations ;  and  even  by  long-continued  anxiety. 
It  is  still  more  notorious  that  the  consumptive  diathesis  is 
conveyed  from  parent  to  child.     Unless,  then,  a  distinction 


HEREDITY.  251 

be  assumed  between  constitutional  consumption  and  con- 
sumption induced  by  unwholesome  conditions — unless  it  bo 
asserted  that  consumption  of  unknown  origin  is  transmiss- 
ible, while  functionally-produced  consumption  is  not  ;  it 
must  be  admitted  that  those  changes  of  structure  from  which 
the  consumptive  diathesis  results,  may  be  caused  in  parents 
by  changes  of  function,  and  may  be  inherited  by  their  chil- 
dren. Most  striking  of  all,  however,  is  the  fact  lately 
brought  to  light,  that  functional  disorders  artificially  estab- 
lished, may  be  conveyed  to  offspring.  Some  few  years  since 
M.  Brown-Sequard,  in  the  course  of  inquiries  into  the  nature 
and  causes  of  epilepsy,  hit  on  a  method  by  which  epilepsy 
could  be  originated.  Guinea-pigs  were  the  creatures  on 
which,  chiefly,  he  experimented  ;  and  eventually,  he  disco- 
vered the  remarkable  fact,  that  the  young  of  these  epileptic 
guinea-pigs  were  epileptic :  the  functionally-established 
epilepsy  in  the  parents,  became  constitutional  epilepsy  in  the 
offspring.  Here  we  have  an  instance  which,  standing  even 
alone,  decides  the  question.  We  have  a  special  form  of  nervous 
action,  not  caused  by  any  natural  variation  of  structure  that 
had  arisen  spontaneously  in  the  organism,  but  one  caused 
by  a  certain  incidence  of  external  forces.  We  have  this 
special  form  of  nervous  action  becoming  confirmed  by  re- 
petition :  the  fits  are  more  and  more  easily  induced — there  is 
established  the  epileptic  habit.  That  is  to  say,  the  connected 
nervous  actions  constituting  a  fit,  produce  in  the  nervous 
system  such  changes  of  structure,  that  subsequent  connected 
nervous  actions  of  like  kind,  follow  one  another  with  increased 
readiness.  And  that  this  epileptic  habit  is  inherited,  proves 
conclusively  that  these  structural  modifications  worked  by 
functional  modifications,  are  impressed  on  the  whole  organism 
in  such  way  as  to  affect  the  reproductive  centres,  and  cause 
them  to  unfold  into  organisms  that  exhibit  like  modifications. 
Evidence  nearly  allied  to  this,  and  scarcely  less  significant, 
is  furnished  by  that  transmission  of  general  nervousness,  no- 
ticed in  the  last  section.     Nervousness  is  especially  common 


252  THE    INDUCTIONS   OF    BIOLOOT. 

among  classes  of  people  who  tax  their  brains  much.  Among 
these  classes,  we  daily  see  this  constitutional  modification 
produced  by  excess  of  function,  in  men  whose  progenitors 
wrere  not  nervous ;  and  the  children  of  such  men  habitually 
inherit  more  or  less  of  the  modification. 

.  §  83.  Two  modified  manifestations  of  Heredity  remain  to  be 
noticed.  The  one  is  the  re-ajjpearance  in  offspring,  of  traits 
not  borne  by  the  parents,  but  borne  by  the  grandparents  or  by 
remoter  ancestors.  The  other  is  the  limitation  of  Heredity  by 
sex — the  restriction  of  certain  transmitted  peculiarities  to 
offspring  of  the  same  sex  as  the  parent  possessing  these 
peculiarities. 

Atavism,  which  is  the  name  given  to  the  recurrence  of 
ancestral  traits,  is  proved  by  many  and  varied  facts.  In  the 
picture-galleries  of  old  families,  and  on  the  monumental 
brasses  in  the  adjacent  churches,  are  often  seen  types  of 
feature  that  are  still,  from  time  to  time,  repeated  in  members  of 
these  families.  It  is  matter  of  common  remark  that  some  con- 
stitutional diseases,  such  as  gout  and  insanity,  after  missing  a 
generation,  will  show  themselves  in  the  next.  Dr  Struthers, 
in  his  above-quoted  paper  on  "  Variation  in  the  Number  of 
Fingers  and  Toes,  and  of  the  Phalanges,  in  Man,"  gives  cases 
of  malformations  that  were  common  to  grandparent  and 
grandchild,  but  of  which  the  parent  had  no  trace.  M.  Girou 
(as  quoted  by  Mr  Sedgwick)  says — "  One  is  often  surprised 
to  see  lambs  black,  or  spotted  with  black,  born  of  ewes  and 
rams  with  white  wool,  but  if  one  takes  the  trouble  to  go 
back  to  the  origin  of  this  phenomenon,  it  is  found  in  the  an- 
cestors." Instances  still  more  remarkable,  in  which  the  re- 
moteness of  the  ancestors  copied  is  very  great,  are  given  by 
Mr  Darwin.  He  points  out  that  in  crosses  between  varieties 
of  the  pigoon,  there  will  sometimes  re-appear  the  plumage  of 
the  original  rock-pigeon,  from  which  these  varieties  descend- 
ed ;  and  he  instances  the  faint  zebra-like  markings  occasion 
ally  traceable  in  lorses,  as  having  probably  a  like  meaning 


HEREDITY.  253 

The  limitation  of  Heredity  by  sex,  cannot  yet  be  regarded 
as  established.  While  in  many  cases  it  seems  clearly  mani- 
fested ;  it  is  in  other  cases  manifested  to  a  very  small  degree, 
if  at  all.  In  Mr  Sedgwick's  essays,  already  named,  will  be 
found  evidence  implying  that  there  exists  some  such  tendency 
to  limitation,  which  does  or  does  not  show  itself  distinctly, 
according  to  the  nature  of  the  organic  modification  to  be 
conveyed.  But  more  facts  must  be  collected  before  any 
positive  conclusion  can  be  reached. 

§  8-1.  A  positive  explanation  of  Heredity  is  not  to  be  expected 
inthepresent  state  of  Biology.  We  can  look  for  nothing  beyond 
a  simplification  of  the  problem  ;  and  a  reduction  of  it  to  the 
same  category  with  certain  other  problems  which  also  admit 
of  hypothetical  solution  only.  If  an  hypothesis  which  certain 
other  wide-spread  phenomena  have  already  thrust  upon  us, 
can  be  shown  to  render  the  phenomena  of  Heredity  more  in- 
telligible than  the}r  at  present  seem,  we  shall  have  reason  to 
entertain  it.  The  applicability  of  any  method  of  interpreta- 
tion to  two  different  but  allied  classes  of  facts,  is  evidence  of 
its  truth. 

The  power  which  organisms  display  of  reproducing  lost 
parts,  we  saw  to  be  inexplicable  except  on  the  assumption 
that  the  units  of  which  any  organism  is  built  have  an  innate 
tendency  to  arrange  themselves  into  the  shape  of  that  organ- 
ism (§  65).  We  inferred  that  these  units  must  be  the  pos- 
sessors of  special  polarities,  resulting  from  their  special  struc- 
tures ;  and  that  by  the  mutual  play  of  their  polarities  they  are 
compelled  to  take  the  form  of  the  species  to  which  they  belong. 
And  the  instance  of  the  Begonia  phyllomaniaca  left  us  no 
escape  from  the  admission  that  the  ability  thus  to  arrange 
themselves,  is  latent  in  the  units  contained  in  every  undiffer- 
entiated cell.  Quite  in  harmony  with  this  conclusion, 
are  certain  implications  since  noticed,  respecting  the  characters 
of  sperm-cells  and  germ-cells.  We  saw  sundry  reasons  for 
rejecting  the  supposition  that  these  are  highly-specialized  cells 


254  THE   INDUCTIONS   OF    BIOLOGY. 

and  for  accepting  the  opposite  supposition,  that  they  are  cells 
differing  from  others  rather  in  being  unspecialized.  And  here 
the  assumption  to  which  we  seem  driven  by  the  ensemble  of 
the  evidence,  is,  that  sperm-cells  and  germ-cells  are  essentially 
nothing  more  than  vehicles,  in  which  are  contained  small 
groups  of  the  physiological  units  in  a  fit  state  for  obeying  their 
proclivity  towards  the  structural  arrangement  of  the  species 
they  belong  to. 

Thus  the  phenomena  of  Heredity  are  seen  to  assimilate 
with  other  phenomena  ;  and  the  assumption  which  these 
other  phenomena  thrust  on  us,  appears  to  be  equally 
thrust  on  us  by  the  phenomena  of  Heredity.  We  must  con- 
clude that  the  likeness  of  any  organism  to  either  parent,  is 
conveyed  by  the  special  tendencies  of  the  physiological  units 
derived  from  that  parent.  In  the  fertilized  germ  we  have 
two  groups  of  physiological  units,  slightly  different  in  their 
structures.  These  slightly-different  units,  severally  multiply 
at  the  expense  of  the  nutriment  supplied  to  the  unfolding  germ 
— each  kind  moulding  this  nutriment  into  units  of  its  own 
type.  Throughout  the  process  of  evolution,  the  two  kinds  of 
units,  mainly  agreeing  in  their  polarities  and  in  the  form 
which  they  tend  to  build  themselves  into,  but  having  m:\ior 
differences,  work  in  unison  to  produce  an  organism  of  the 
species  from  which  they  were  derived,  but  work  in  antago  asm 
to  produce  copies  of  their  respective  pa  rent- organisms.  And 
hence  ultimately  results,  an  organism  in  which  traits  of  the 
one  are  mixed  with  traits  of  the  other. 

If  the  likeness  of  offspring  to  parents  is  thus  determined,  it 
becomes  manifest,  a  priori,  that  besides  the  transmission  of 
generic  and  specific  peculiarities,  there  will  be  a  transmis- 
sion of  those  individual  peculiarities  which,  arising  without 
assignable  causes,  are  classed  as  "  spontaneous."  For  if  the 
assumption  of  a  special  arrangement  o^  parts  by  an  organism, 
is  due  to  the  pi'oclivity  of  its  physiological  units  towards 
that  arrangement ;  then  the  assumption  of  an  arrangement 
of  parts  slightly  different  from  that  of  the  species;  unplios 


HEREDITY.  255 

physiological  units  slightly  unlike  those  of  the  species  ;  and 
these  slightly- unlike  physiological  units,  communicated 
through  the  medium  of  sperm-cell  or  germ-cell,  will  tend,  in 
the  offspring,  to  build  themselves  into  a  structure  similarly 
diverging  from  the  average  of  the  species. 

It  is  not  equally  manifest,  a  priori,  however,  that  on  this  hy- 
pothesis, alterations  of  structure  caused  by  alterations  of  func- 
tion, must  be  transmitted  to  offspring.  It  is  not  obvious  that 
change  in  the  form  of  a  part,  caused  by  changed  action,  in- 
volves such  change  in  the  physiological  units  throughout  the 
organism,  that  these,  when  groups  of  them  are  thrown  off  in 
the  shape  of  reproductive  centres,  will  unfold  into  organisms 
that  have  this  part  similarly  changed  in  form.  Indeed,  when 
treating  of  Adaptation  (§  69),  we  saw  that  an  organ  modified 
by  increase  or  decrease  of  function,  can  but  slowly  so  re-act 
on  the  system  at  large,  as  to  bring  about  those  correlative 
changes  required  to  produce  a  new  equilibrium ;  and  yet  only 
when  such  new  equilibrium  has  been  established,  'can  we  ex- 
pect it  to  he  fully  expressed  in  the  modified  physiological  units 
of  which  the  organism  is  built — only  then  can  we  count 
on  a  complete  transfer  of  the  modification  to  descendants. 
Nevertheless,  that  changes  of  structure  caused  by  changes 
of  action,  must  also  be  transmitted,  however  obscurely,  from 
one  generation  to  another,  appears  to  be  a  deduction  from 
first  principles — or  if  not  a  specific  deduction,  still,  a  general 
implication.  For  if  an  organism  A,  has,  by  any  peculiar 
habit  or  condition  of  life,  been  modified  into  the  form  A,  it 
follows  inevitably,  that  all  the  functions  of  A',  reproductive 
function  included,  must  be  in  some  degree  different  from  the 
functions  of  A.  An  organism  being  a  combination  of 
rhythmically-acting  parts  in  moving  equilibrium,  it  is  im- 
possible to  alter  the  action  and  structure  of  any  one  part, 
without  causing  alterations  of  action  and  structure  in  all  the 
rest;  just  as  no  member  of  the  Solar  System  could  be  modi- 
fied in  motion  or  mass,  without  producing  re-arrangementa 
throughout  the  whole  Solar  System.    And  if  the  organism  A 


256  THE    INDUCTIONS    OF    BIOLOGY. 

when  changed  to  A',  must  be  changed  in  all  its  functions : 
then  the  offspring  of  A'  cannot  be  the  same  as  they  would 
have  been  had  it  retained  the  form  A.     It  involves  a  denial 
of  the  persistence  of  force  to  say  that  A  may  be  changed 
into  A',  and  may  yet  beget  offspring  exactly  like  those  it 
would  have  begotten  had  it  not  been  so  changed.     That  the 
change  in  the  offspring  must,  other  things  equal,  be  in  the 
same  direction  as  the  change  in  the  parent,  we  may  dimly  see 
is  implied  by  the  fact,  that  the  change  propagated  throughout 
the  parental  system   is   a   change  towards  a  new   state  of 
equilibrium — a  change  tending  to  bring  the  actions  of  all 
organs,  reproductive  included,  into  harmony  with  these  new 
actions.      Or,    bringing    the    question   to  its   ultimate   and 
simplest  form,  we  may  say  that  as,  on  the  one  hand,  phy- 
siological units  will,  because  of  their  special  polarities,  build 
themselves  into  an  organism  of  a  special  structure  ;    so.  on 
the  other  hand,  if  the  structure  of  this  organism  is  modified 
by  modified  function,  it   will  impress  some  corresponding 
modification  on  the  structures  and  polarities  of  its  units.    The 
units  and  the  aggregate  must  act  and  re-act  on  each  other. 
The  forces  exercised  by  each  unit  on  the  aggregate  and  by 
the  aggregate  on  each  unit,  must  ever  tend  towards  a  balance. 
If  nothing  prevents,  the  units  will  mould  the  aggregate  into 
a  form  in  equilibrium  with  their  pre-existing  polarities.     If. 
contrariwise,  the  aggregate  is  made  by  incident  actions  to 
take  a  new  form,  its  forces  must  tend  to  re-mould  the  units 
into  harmony  with   this   new   form.     And   to  say  that  the 
physiological  units  are  in  any  degree  so  re- moulded  as  to  bring 
their  polar  forces  towards  equilibrium  with  the  forces  of  the 
modified  aggregate,  is  to  say  that  when  separated  in  the 
shape  of  reproductive  centres,  these  units  will  tend  to  build 
themselves  up  into  an  aggregate  modified  in  the  same  di- 
rection. 


CHAPTER   IX. 
VARIATION. 

§  85  Equally  conspicuous  with  the  truth  that  every  organ- 
ism bears  a  general  likeness  to  its  parents,  is  the  truth  that 
no  organism  is  exactly  like  either  parent.  Though  similar 
to  both  in  generic  and  specific  traits,  and  usually,  too,  in  those 
traits  which  distinguish  the  variety,  it  diverges  in  numer- 
ous traits  of  minor  importance.  No  two  plants  are  indistin- 
guishable ;  and  no  two  animals  are  without  differences. 
Variation  is  co-extensive  with  Heredity. 

The  degrees  of  variation  have  a  wide  range.  There  are 
deviations  so  small  as  to  be  not  easily  detected  ;  and  there 
are  deviations  great  enough  to  be  called  monstrosities.  In 
plants,  we  may  pass  from  cases  of  slight  alteration  in  the 
shape  or  texture  of  a  leaf,  to  cases  where,  instead  of  a  flower 
with  its  calyx  above  the  seed-vessel,  there  is  produced  a  flower 
with  its  calyx  below  the  seed-vessel ;  and  while  in  one 
animal,  there  arises  a  scarcely  noticeable  unlikeness  in  the 
length  or  colour  of  the  hair,  in  another,  an  organ  is  absent, 
or  a  supernumerary  organ  appears.  Though  small  variations 
are  by  far  the  most  general,  yet  variations  of  considerable 
magnitude  are  not  uncommon  ;  and  even  those  variations 
constituted  by  additions  or  suppressions  of  parts,  are  not  so 
rare  as  to  be  excluded  from  the  list  of  causes  by  which 
organic  forms  are  changed.  Cattle  without  horns  are  fre- 
quent.    Of  sheep  there  are  horned  breeds  and  breeds  that 


268  THE    INDUCTIONS   OF    BIOLOGY. 

have  lost  their  horns.  At  one  time,  there  existed  in  Scot- 
land a  race  of  pigs  with  solid  feet  instead  of  cleft  feet.  In 
pigeons,  according  to  Mr  Darwin,  "  the  number  of  the  cau- 
dal and  sacral  vertebrae  vary ;  as  does  the  number  of  the 
ribs,  together  with  their  relative  breadth  and  tha  presence  of 
processes." 

That  variations  both  small  and  large  which  arise  without 
any  specific  assignable  cause,  tend  to  become  hereditary,  was 
shown  in  the  last  chapter.  Indeed  the  evidence  which  proves 
Heredity  in  its  smaller  manifestations,  is  the  same  evidence 
which  proves  Variation  ;  since  it  is  only  when  there  occur  vari- 
ations, that  the  inheritance  of  anything  beyond  the  structural 
peculiarities  of  the  species,  can  be  proved.  It  remains  here, 
however,  to  be  observed,  that  the  transmission  of  variations 
is  itself  variable ;  and  that  it  varies  both  in  the  direction  of 
decrease  and  in  the  direction  of  increase.  An  individual  trait 
of  one  parent,  may  be  so  counteracted  by  the  influence  of  the 
other  parent,  that  it  may  not  appear  in  the  offspring ;  or  not 
being  so  counteracted,  the  offspring  may  possess  it,  perhaps 
in  an  equal  degree  or  perhaps  in  a  less  degree  ;  or  the  off- 
spring may  exhibit  the  trait  in  even  a  still  higher  degree. 
Of  the  illustrations  of  this,  one  must  suffice.  I  quote  it  from 
the  essay  by  Dr  Struthers,  referred  to  in  the  last  chapter. 

"  The  great-great-grandmother,  Esther  P (who  mar- 
ried A L ),  had  a  sixth  little  finger  on  one  hand.     Of 

their  eighteen  children  (twelve  daughters  and  six  sons),  oniy 
one  (Charles)  is  known  to  have  had  digital  variety.  We 
have  the  history  of  .the  descendants  of  three  of  the  sons, 
Andrew,  Charles,  and  James. 

"  (1.)  Andrew  L had  two  sons,  Thomas  and  Andrew  ; 

and  Thomas  had  two  sons  all  without  digital  variety.  Here 
we  have  three  successive  generations  without  the  variety 
possessed  by  the  great- grandmother  showing  itself. 

"(2.)  James  L ,  who  was  normal,  had  two  sons  and 

seven  daughters,  also  normal.  One  of  the  daughters  became 
Mrs  J (one  of  the  informants),  and  had  three  daughters 


VARIATION.  259 

and  five  sons,  all  normal  except  one  of  the  sons,  James  J , 

now  net.  17,  who  had  six  fingers  on  each  hand.     *     *     * 

"  In  tliis  branch  of  the  descendants  of  Esther,  we  see  it 
passing  over  two  generations  and  reappearing  in  one  member 
of  the  third  generation,  and  now  on  both  hands. 

"  (3.)  Charles  L ,  the  only  child  of  Esther  who  had 

digital  variety,  had  six  fingers  on  each  hand.  He  had  three 
eons,  James,  Thomas,  and  John,  all  of  whom  were  born  with 
six  fingers  on  each  hand,  while  John  has  also  a  sixth  toe  on 
one  foot.  He  had  also  five  other  sons  and  four  daughters, 
all  of  whom  were  normal. 

"  (a.)  Of  the  normal  children  of  this,  the  third  generation, 
the  five  sons  had  twelve  sons  and  twelve  daughters,  and  the 
four  daughters  have  had  four  sons  and  four  daughters,  being 
the  fourth  generation,  all  of  whom  were  normal.  A  fifth 
generation  in  this  sub-group  consists  as  yet  of  only  two  boys 
and  two  girls,  who  are  also  normal. 

"  In  this  sub-branch,  we  see  the  variety  of  the  first  gener- 
ation present  in  the  second,  passing  over  the  third  and 
fourth,  and  also  the  fifth  as  far  as  it  has  yet  gone. 

"  (b.)  James  had  three  sons  and  two  daughters,  who  are 
normal. 

"  (c.)  Thomas  had  four  sons  and  five  daughters,  who  are 
normal ;  and  has  two  grandsons,  also  normal. 

"  In  this  sub-branch  of  the  descent,  we  see  the  variety  of 
the  first  generation,  showing  itself  in  the  second  and  third, 
and  passing  over  the  fourth,  and  (as  far  as  it  yet  exists) 
the  fifth  generation. 

"  (d.)  John  L  —  (one  of  the  informants)  had  six  fingers, 
the  additional  finger  being  attached  on  the  outer  side,  as  in 
the  case  of  his  brothors  Jame3  and  Thomas.  All  of  them 
had  the  additional  digits  removed.  John  has  also  a  sixth 
toe  on  one  foot,  situated  on  the  outer  side.  The  fiftn  and 
sixth  toes  have  a  common  proximal  phalanx,  and  a  common 
integument  invests  the  middle  and  distal  phalanges,  each 
having  a  separate  nail. 


<J60  THE    INDUCTIONS   OF    BIOLOGY. 

"  John  L has  a  son  who  is  normal,  and  a  daughter 

Jane,  who  was  born  with  six  fingers  on  each  hand  and  six  toea 
on  each  foot.  The  sixth  fingers  were  removed.  The  sixth 
toes  are  not  wrapped  with  the  fifth  as  in  her  father's  case, 
but  are  distinct  from  them.  The  son  has  a  son  and  daughter, 
who,  like  himself,  are  normal. 

"  In  this,  the  most  interesting  sub-branch  of  the  descent, 
we  see  digital  increase,  which  appeared  in  the  first  generation 
on  one  limb,  appearing  in  the  second  on  two  limbs,  the 
hands  ;  in  the  third  on  three  limbs,  the  hands  and  one  foot ; 
in  the  fourth  on  all  the  four  limbs.  There  is  as  yet  no  fifth 
generation  in  uninterrupted  transmission  of  the  variety. 
The  variety  does  not  yet  occur  in  any  number  of  the  fifth 
generation  of  Esther's  descendants,  which  consists,  as  yet, 
only  of  three  boys  and  one  girl,  whose  parents  were  normal, 
and  of  two  boys  and  two  girls,  whose  grandparents  were 
normal.  It  is  not  known  whether  in  the  case  of  the  great- 
great-grandmother,  Esther  P ,  the  variety  was  original 

or  inherited."* 

§  86.  Where  there  i8  great  uniformity  among  the  mem- 
bers of  a  species,  the  divergences  of  offspring  from  the 
average  type,  are  usually  small ;  but  where,  among  the 
members  of  a  species,  considerable  unlikenesses  have  once 
been  established,  unlikenesses  among  the  offspring  are  fre- 
quent and  great.  Wild  plants  growing  in  their  natural 
habitats,  are  uniform  over  large  areas,  and  maintain  from 
generation  to  generation  like  structures  ;  but  when  cultiva- 
tion has  caused  appreciable  differences  among  the  members 
}f  any  species  of  plant,  extensive  and  numerous  deviations 
are  apt  to  arise.     Similarly,  between  wild  and  domesticated 

*  This  remarkable  case  appears  to  militate  against  the  conclusion,  drawn  some 
few  pages  back,  that  the  increase  of  a  peculiarity  by  coincidence  of  "  spontaneous 
variations "  in  successive  generations,  is  very  improbable ;  and  that  the  special 
superiorities  of  musical  composers  cannot  have  thus  arisen.  The  reply  is,  that 
the  extreme  frequency  of  the  occurrence  among  so  narrow  a  class  as  that  of 
musical  composers,  forbids  the  interpretation  „hus  suggested. 


VARIATION.  261 

animals  of  the  same  species,  we  see  the  contrast,  that  though 
the  homogeneous  wild  race  maintains  its  type  with  great  per- 
sistence, the  comparatively  heterogeneous  domestic  race  fre- 
quently produces  individuals  more  unlike  the  average  type 
than  the  parents  are. 

Though  unlikeness  among  progenitors  is  one  antecedent 
cf  variation,  it  is  by  no  means  the  sole  antecedent.  Were 
it  so,  the  young  ones  successively  born  to  the  same  parents 
would  be  alike.  If  any  peculiarity  in  a  new  organism 
were  a  direct  resultant  of  the  structural  differences  between  the 
two  organisms  which  produced  it ;  then  all  subsequent  new 
organisms  produced  by  these  two,  would  show  the  same  pecu- 
liarity. But  we  know  that  the  successive  offspring  have  differ- 
ent peculiarities  :  no  two  of  them  are  ever  exactly  alike. 

One  cause  of  such  structural  variation  in  progeny,  18 
functional  variation  in  parents.  Proof  of  this  is  given  by 
the  fact  that,  among  the  progeny  of  the  same  parents,  there  is 
more  difference  between  those  begotten  under  different  con- 
stitutional states,  than  between  those  begotten  under  the 
same  constitutional  state.  It  is  notorious  that  twins  are 
more  nearly  alike  than  children  borne  in  succession.  The 
functional  conditions  of  the  parents  being  the  same  for  twins, 
but  not  the  same  for  their  brothers  and  sisters  (all  other  ante- 
cedents being  constant)  ;  we  have  no  choice  but  to  admit  that 
variations  in  the  functional  conditions  of  the  parents,  are  the 
antecedents  of  those  greater  unlikenesses  which  their  brothera 
and  sisters  exhibit. 

Some  other  antecedent  remains,  however.  The  parents 
being  the  same,  and  their  constitutional  states  the  same,  va- 
riation, more  or  less  marked,  still  manifests  itself.  Plants 
grown  from  seeds  out  of  one  pod,  and  animals  produced  at 
one  birth,  are  not  alike ;  and  sometimes  differ  considerably. 
In  a  litter  of  pigs  or  of  kittens,  we  rarely  see  uniformity  of 
markings ;  and  occasionally,  there  are  important  structural 
contrasts.  I  have  myself  recently  been  shown  a  litter  of 
Newfoundland  puppies,  some  of  which  had    four    digits  to 


262  THE    INDUCTIONS    OF   BIOLOGY. 

their  feet,  while  in  others,  there  was  present  on  each  hind- foot) 
what  is  called  the  "  dew-claw  " — a  rudimentary  fifth  digit. 

Thus,  induction  points  to  three  causes  of  variation,  all  in 
action  together.  We  have  heterogeneity  among  progenitors, 
which,  did  it  act  uniformly  and  alone  in  generating,  by  composi- 
tion of  forces,  new  deviations,  would  impress  such  new  devia- 
tions to  the  same  extent  on  all  offspring  of  the  same  parents  ; 
which  it  does  not.  We  have  functional  variation  in  the  pa- 
rents, which,  acting  either  alone  or  in  combination  with  the  pre- 
ceding cause,  would  entail  like  variations  on  all  young  ones 
simultaneously  produced ;  which  it  does  not.  And  there  is 
consequently  some  third  cause  of  variation,  yet  to  be  found, 
which  acts  along  with  the  structural  and  functional  variations 
of  ancestors  and  parents. 

§  87  Already,  in  the  last  section,  there  has  been  implied 
some. relation  between  variation  and  the  action  of  external 
conditions.  The  above-cited  contrast,  between  the  uniformity 
of  wild  species  and  the  multiformity  of  the  same  species 
when  cultivated  or  domesticated,  thrusts  this  truth  upon  us. 
.Respecting  the  variations  of  plants,  Mr  Darwin  remarks 
that  "  '  sports '  are  extremely  rare  under  nature,  but  far  from 
rare  undei  cultivation."  Others  who  have  studied  the  matter 
assert,  that  if  a  species  of  plant  which,  up  to  a  certain  time, 
has  maintained  great  uniformity,  once  has  its  constitution 
thoroughly  disturbed,  it  will  go  on  varying  indefinitely. 
Though,  in  consequence  of  the  remoteness  of  the  periods  at 
which  they  were  domesticated,  there  is  a  lack  of  positive 
proof  that  our  extremely  variable  domestic  animals  have  be- 
come variable  under  the  changed  conditions  implied  by  do- 
mestication, having  been  previously  constant ;  yet  competent 
judges  do  not  doubt  that  this  has  been  the  case. 

Now  the  constitutional  disturbance  which  precedes  varia- 
tion, can  be  nothing  else  than  an  overthrowing  of  the  pre- 
established  equilibrium  of  functions.  Transferring  a  plant 
from  forest  lands  to  a  ploughed  field  or  a  manured  garden,  ia 


VARIATION.  203 

altering  the  balance  of  forces  to  which  it  has  been  hitherto 
subject ;  by  supplying  it  with  different  proportions  of  the 
assimilable  matters  it  requires,  and  taking  away  some  of  the 
positive  impediments  to  its  growth  which  competing  wild 
plants  before  offered.  An  animal  taken  from  woods  or  plains, 
where  it  lived  on  wild  food  of  its  own  procuring,  and  placed 
under  restraint,  while  artificially  supplied  with  food  not  quite 
like  what  it  had  before,  is  an  animal  subject  to  new  outer  ac- 
tions, to  which  its  inner  actions  must  be  re-adjusted.  From 
the  general  law  of  equilibration  we  found  it  to  follow,  that 
"  the  maintenance  of  such  a  moving  equilibrium  "  as  an  or- 
ganism displays,  "  requires  the  habitual  genesis  of  internal 
forces  corresponding  in  number,  directions,  and  amounts,  tc 
the  external  incident  forces  —  as  many  inner  functions, 
single  or  combined,  as  there  are  single  or  combined  outer  ac 
tions  to  be  met "  (First  Principles,  %  133)  ;  and  more  recently 
(§  27),  we  have  seen  that  Life  itself  is  "the  definite  combin- 
ation of  heterogeneous  changes,  both  simultaneous  and  suc- 
cessive, in  correspondence  with  external  co-existences  and 
sequences."  Necessarily,  therefore,  an  organism  exposed  to  a 
permanent  change  in  the  arrangement  of  outer  forces,  must 
undergo  a  permanent  change  in  the  arrangement  of  inner 
forces.  The  old  equilibrium  must  be  destroyed ;  and  a  new 
equilibrium  must  be  established.  There  must  be  func- 
tional perturbations,  ending  in  a  re-adjusted  balance  of 
functions. 

If,  then,  change  of  conditions  is  the  only  known  cause  by 
which  the  original  homogeneity  of  a  species  is  destroyed  ; 
and  if  change  of  conditions  can  affect  an  organism  only  by 
altering  its  functions ;  it  follows  that  alteration  of  func- 
tions is  the  only  known  internal  cause  to  which  the  com- 
mencement of  variation  can  be  ascribed.  That  such  minoi 
functional  changes  as  parents  undergo  from  year  to  year,  are 
influential  on  the  offspring,  we  have  seen  to  be  proved  by 
the  greater  unlikeness  that  exists  between  children  born  to 
the    same    parents  at    different  times,  than  exists  between 


264  THE    INDUCTIONS   OF    BIOLOGY. 

twins.  And  here  we  seem  forced  to  conclude,  thai  the  larger 
functional  variations  produced  by  greater  external  changes, 
are  the  initiators  of  those  structural  variations  which,  when 
once  commenced  in  a  species,  lead  by  their  combinations  and 
antagonisms  to  multiform  results.  Whether  they  are  or 
are  not  the  direct  initiators,  they  must  still  be  the  indirect 
initiators. 

§  88.  That  they  are  not  in  all  cases,  or  even  in  most  cases, 
the  direct  initiators,  is  clear.  Were  they  so,  those  unlike- 
nesses  which  exist  between  plants  that  grow  from  seeds  out 
of  the  same  seed-vessel,  or  between  animals  belonging  to  the 
same  litter,  would  be  inexplicable.  Here,  all  the  antecedents, 
structural  and  functional,  appear  to  be  alike  for  each  of  the 
new  organisms.  Any  deviations  caused  by  structural  con- 
trasts or  functional  disturbances  in  the  parents,  must  be 
equally  shared  in  by  all  simultaneously-produced  offspring. 
Hence,  an  explanation  of  the  variations  arising  under  such 
conditions,  has  still  to  be  sought. 

These  are  the  variations  termed  "  spontaneous."  Not  that 
those  who  apply  to  them  this  word  or  some  equivalent,  mean 
to  imply  that  they  are  uncaused.  Mr  Darwin  expressly 
guards  himself  against  such  an  interpretation.  He  says  : — 
"  I  have  hitherto  sometimes  spoken  as  if  the  variations — so 
common  and  multiform  in  organic  beings  under  domestica- 
tion, and  in  a  lesser  degree  in  those  in  a  state  of  nature — had 
been  due  to  chance.  This,  of  course,  is  a  wholly  incorrect 
expression,  but  it  serves  to  acknowledge  plainly  our  ignorance 
of  the  cause  of  each  particular  variation."  Not  only,  how- 
ever, do  I  hold,  in  common  with  Mr  Darwin,  that  there  must 
be  some  cause  for  these  apparently-spontaneous  variations ; 
but  it  seems  to  me  that  a  definite  cause  is  assignable.  I 
think  it  may  be  shown  that  unlikenesses  must  necessarily 
arise  between  the  new  individuals  simultaneously  produced 
by  the  same  parents.     Instead  of  the  occurrence  of  such 


VARIATION.  2Go 

variations  being  inexplicable,  we  shall  presently  see  that  the 
absence  of  them  would  be  inexplicable. 

In  any  series  of  dependent  changes,  a  small  initial  difference 
ofren  works  a  marked  difference  in  the  results.  The  mode  in 
which  a  particular  breaker  bursts  on  the  beach,  may  determine 
whetherthe  seed  of  some  foreign  plant  which  it  bears,  is  oris  not 
stranded — may  cause  the  presence  or  absence  of  this  plant  from 
the  Flora  of  the  land;  and  may  so  affect,  for  millions  of  years,  in 
countless  ways,  the  living  creatures  throughout  the  land.  A 
single  touch,  by  introducing  into  the  body  some  morbid  mat- 
ter, may  set  up  an  immensely-involved  set  of  functional  dis- 
turbances and  structural  alterations.  The  whole  tenor  of  a  life 
may  be  changed  by  a  word  of  advice  ;  or  a  glance  may 
determine  an  action  which  alters  thoughts,  feelings,  and 
deeds  throughout  a  long  series  of  years.  In  those  still  more 
involved  combinations  of  changes  which  societies  exhibit, 
this  truth  is  still  more  conspicuous.  A  hair's-breadth  differ- 
ence in  the  direction  of  some  soldier's  musket  at  the  battle  of 
Areola,  by  killing  Napoleon,  might  have  changed  events 
throughout  Europe :  though  the  social  organization  in  each 
European  country,  would  have  been  now  very  much  what  it 
is,  yet  in  countless  details  it  would  have  been  different. 

Illustrations  like  these,  with  which  pages  might  be  filled, 
prepare  us  for  the  conclusion,  that  organisms  produced  by 
the  same  parents,  at  the  3ame  time,  must  be  more  or  less 
differentiated  both  by  insensible  initial  differences,  and  by 
slight  differences  in  the  conditions  to  which  they  are  subject 
during  their  evolution.  We  need  not,  however,  rest  with 
assuming  such  initial  differences :  the  necessity  of  them  i& 
demonstrable.  The  individual  germ-cells  which,  in  succes- 
sion or  simultaneously,  are  separated  from  the  same  parent, 
can  never  be  exactly  alike ;  nor  can  the  sperm-cells  which 
lertilize  them.  When  treating  of  the  instability  of  the 
homogeneous  (First  Principles,  §  109),  we  saw  that  no  two 
]iarts  of  any  aggregate,  can   be  similarly  conditioned  with 

IS 


266 


THE    INDUCTIONS    OF    BIOLOGY. 


respect  to  incident  forces ;  and  that  being  subject  to  forces 
that  are  more  or  less  unlike,  they  must  become  more  or  less 
unlike.  Hence,  no  two  ova  in  an  ovarum  or  ovules  in  a 
seed-vessel— no  two  spermatozoa  or  pollen-cells,  can  be 
identical.  Whether  or  not  there  arise  other  contrasts,  there 
are  certain  to  arise  quantitative  contrasts  ;  since  the  process 
of  nutrition  cannot  be  absolutely  alike  for  all.  The  repro- 
ductive centres  must  begin  to  differentiate  from  the  very 
outset.  Such  being  the  necessities  of  the  case,  what 

will  happen  on  any  successive  or  simultaneous  fertilizations  ? 
There  will  inevitably  result  more  or  less  unlikeness  between 
the  combined  parental  influences  in  every  instance.  Quan- 
titative differences  among  the  sperm-cells  and  among  the 
germ-cells,  will  insure  this.  Grant  that  the  number  of 
physiological  units  contained  in  any  one  reproductive  cell,  can 
rarely  if  ever  be  exactly  equal  to  the  number  contained 
in  any  other,  ripened  at  the  same  time  or  at  a  different  time  ; 
and  it  follows  that  among  the  fertilized  germs  produced  by 
the  same  parents,  the  physiological  units  derived  from  each 
parent  will  bear  a  different  numerical  ratio  to  each  other  in 
every  case.  If  now  the  parents  are  constitutionally  alike, 
that  is,  alike  in  the  polarities  of  their  physiological  units, 
the  variation  in  the  ratio  between  the  physiological  units 
they  severally  bequeath  to  the  fertilized  germs,  cannot  cause 
unlikenesses  among  the  offspring.  But  if  otherwise,  no  two 
of  the  offspring  can  be  alike.  In  every  case,  the  small  initial 
difference  in  the  proportions  of  the  slightly-unlike  units, 
will  lead,  during  evolution,  to  a  continual  multiplication  of 
differences  :  the  insensible  divergence  at  the  outset,  will  gener- 
ate sensible  divergences  at  the  conclusion.  Possi- 
bly some  may  hence  infer,  that  though,  in  such  case,  the 
offspring  must  differ  somewhat  from  each  other  and  from 
both  parents  ;  yet  that  in  every  one  of  them  there  must 
result  a  homogeneous  mixture  of  the  traits  of  the  two  parents. 
A  little  consideration  shows  that  the  reverse  is  inferable.  If, 
throughout  the  process  of   development,  the    physiological 


VARIATION.  2G7 

emits  derived  from  each  parent,  preserved  the  same  ratio  to 
each  other  in  all  parts  of  the  growing  organism,  each  organ 
would  show  as  much  as  every  other,  the  influence  of  either 
parent.  But  we  know,  a  priori,  that  no  such  uniform  dis- 
tribution is  possible.  It  has  been  shown  (First  Principles, 
§  123),  that  in  any  mixed  aggregate  of  units,  segregation 
must  inevitably  go  on.  Incident  forces  will  tend  ever  to 
cause  separation  of  the  two  orders  of  units  from  each  other — 
will  integrate  groups  of  the  one  order  in  one  place,  and 
groups  of  the  other  order  in  another  place.  Hence  there 
must  arise,  not  a  homogeneous  mean  between  the  two 
parents ;  but  a  mixture  of  organs,  some  of  which  mainly 
follow  the  one  parent  and  some  the  other.  And  this  is  the 
kind  of  mixture  which  observation  shows  us. 

Still  it  may  be  fairly  objected,  that  however  the  attributes 
of  the  two  parents  are  variously  mixed  in  their  several 
offspring,  they  must  in  all  the  offspring  fall  between  the 
extremes  displayed  in  the  parents.  In  no  characteristic 
could  one  of  the  young  exceed  both  parents,  were  there  no 
cause  of  "  spontaneous  variation  "  but  the  one  alleged.  Evi- 
dently, then,  there  is  a  cause  yet  unfound. 

§  89.  Thus  far  we  have  contemplated  the  process  under 
its  simplest  aspect.  While  we  have  assumed  the  two  parents 
to  be  somewhat  unlike,  we  have  assumed  that  each  parent 
has  a  homogeneous  constitution — is  built  up  of  physiologi- 
cal units  that  are  exactly  alike.  But  in  no  case  can  such  a 
homogeneity  exist.  Each  parent  had  parents  that  were  more 
or  less  contrasted — each  parent  inherited  at  least  two  orders 
of  physiological  units,  not  quite  identical.  Here  then  wc 
have  a  further  cause  of  variation.  The  sperm-cells  or  germ- 
cells  which  any  organism  produces,  will  differ  from  each 
other  not  quantitatively  only,  but  qualitatively.  Of  the 
slightly-unlike  physiological  units  bequeathed  to  an  organism, 
its  reproductive  cells  cannot  habitually  contain  the  same  pro- 
portions ;  and  we  may  expect  the  proportions  to  vary  not 


2G8 


THE    INDUCTIONS   OF    BIOLOGV. 


slightly  but  greatly.  Just  as,  during  the  evolution  of  an  or* 
ganism,  the  physiological  units  derived  from  the  two  parenta 
tend  to  segregate,  and  produce  likeness  to  the  male  parent  in 
this  feature  and  to  the  female  parent  in  that ;  so,  during  the 
formation  of  reproductive  cells  by  such  organism,  there  will 
arise  in  one  cell  a  predominance  of  the  physiological  units 
derived  from  one  parent,  and  in  another  cell  a  predominance 
of  the  physiological  units  derived  from  the  other  parent.  The 
instability  of  the  homogeneous  forbids  us  to  assume  an  even 
distribution  of  the  two  orders  of  units  in  all  the  reproductive 
cells.  And  inequalities  once  arising  among  them,  must  tend 
ever  to  become  more  marked  ;  since,  wherever  units  of  a 
given  order  have  begun  to  segregate,  the  process  of  differenti- 
ation and  integration  tends  to  segregate  them  more  and  more. 
Thus,  then,  every  fertilized  germ,  besides  containing  different 
amounts  of  the  two  parental  influences,  will  contain  different 
kinds  of  influences — this  having  received  a  marked  impress 
from  one  maternal  or  paternal  ancestor,  and  that  from  an- 
other. 

Here,  then,  we  have  a  clue  to  the  multiplied  variations,  and 
sometimes  extreme  variations,  that  arise  in  races  which  have 
once  begun  to  vary.  Amid  countless  different  combinations 
of  units  derived  from  parents,  and  through  them  from  ances- 
tors, immediate  and  remote — amid  the  various  conflicts  in 
*heir  slightly-different  polarities,  opposing  and  conspiring 
with  each  other  in  all  ways  and  degrees  ;  there  will  from 
time  to  time  arise  special  proportions  causing  special  devi- 
ations. From  the  general  law  of  probabilities  it  is  inferable, 
that  while  these  involved  influences,  derived  from  many  pro- 
genitors, must,  on  the  average  of  cases,  obscure  and  partially 
neutralize  one  another  ;  there  must  occasionally  result  such 
combinations  of  them  as  will  produce  considerable  divergences 
from  average  structures  ;  and  at  rare  intervals,  such  com- 
binations as  will  produce  very  marked  divergences.  There  is 
thus  a  correspondence  between  the  inferable  results,  and  the 
results  as  habitually  witnessed. 


VARIATION.  2G9 

§  90.  Still  there  remains  a  difficulty.  It  may  be  said  that 
admitting  functional  change  to  be  the  initiator  of  variation 
— granting  that  the  physiological  units  of  an  organism, 
modified  by  long  subjection  to  new  conditions,  will  tend  to  be- 
come modified  in  such  wav  as  to  cause  change  of  structure  in 
offspring ;  .yet  there  will  still  be  no  cause  of  ihe  supposed 
heterogeneity  among  the  physiological  units  of  different  in- 
dividuals. There  seems  validity  in  the  objection,  that  as  all 
the  members  of  a  species  whose  circumstances  have  been  al- 
tered, will  be  affected  in  the  same  manner,  the  results,  when 
they  begin  to  show  themselves  in  descendants,  will  show  them- 
selves in  the  same  manner :  not  multiform  variations  will 
arise,  but  deviations  all  in  one,direction. 

The  reply  is  simple.  The  members  of  a  species  thus  cir- 
cumstanced, will  not  be  similarly  affected.  In  the  absence  of 
absolute  uniformity  among  them,  the  functional  changes 
caused  in  them  will  be  more  or  less  dissimilar.  Just  as  men 
of  slightly- unlike  dispositions  behave  in  quite  opposite  ways 
under  the  same  circumstances  ;  or  just  as  men  of  slightly- 
unlike  constitutions  get  diverse  disorders  from  the  same 
cause,  and  are  diversely  acted  on  by  the  same  medicine ;  so, 
the  insensibly-differentiated  members  of  a  species  whose  con- 
ditions have  been  changed,  may  at  once  begin  to  undergo 
various  kinds  of  functional  changes.  As  we  have  already 
seen,  small  initial  contrasts  may  lead  to  large  terminal  con- 
trasts. The  intenser  cold  of  the  climate  into  which  a  species 
has  migrated,  may  cause  in  one  individual  increased  con- 
sumption of  food,  to  balance  the  greater  loss  of  heat ;  while 
in  another  individual,  the  new  requirement  7 nay  be  met  by  a 
thicker  growth  of  fur.  Or,  when  meeting  with  the  new  foods 
which  the  new  region  furnishes,  mere  accident  may  deter- 
mine one  member  of  the  species  to  begin  with  one  kind  and 
another  member  with  another  kind  ;  and  hence  may  arise 
established  habits  in  these  respective  members  and  their 
descendants.  Now  when  the  functional  divergences  thus  set 
up  in  sundry  families  of  a  species,  have  lasted  long  enough 


270  THE    INDUCTIONS    OF    BIOLOOV. 

to  affect  their  constitutions  profoundly,  and  to  modify  sorno 
what  the  physiological  units  thrown  off  in  their  reproductive 
cells,  the  divergences  produced  by  these  in  offspring,  will  be 
of  diverse  kinds.  And  the  original  homogeneity  of  constitu- 
tion having  been  thus  destroyed,  variation  may  go  on  with 
increasing  facility.  There  will  result  a  heterogeneous  mix- 
ture of  modifications  of  structure,  caused  by  modifications  of 
function  ;  and  of  still  more  numerous  correlated  modifica- 
tions, indirectly  so  caused.  By  natural  selection  of  the  most 
divergent  forms,  the  unlikenesses  of  parents  will  grow  more 
marked,  and  the  limits  of  variation  wider.  Until  at  length 
the  divergences  of  constitutions  and  modes  of  life,  become 
great  enough  to  lead  to  segregation  of  the  varieties. 

§  91.  That  variations  must  occur,  and  that  they  must  ever 
tend,  both  directly  and  indirectly,  towards  adaptive  modifica- 
tions, are  conclusions  deducible  from  first  principles;  apart 
from  any  detailed  interpretations  like  the  above.  That  the 
state  of  homogeneity  is  an  unstable  state,  we  have  found  to 
be  a  universal  truth.  Each  species  must  pass  from  the  uni- 
form into  the  more  or  less  multiform,  unless  the  incidence  of 
external  forces  is  exactly  the  same  for  all  its  members ;  which 
it  never  can  be.  Through  the  process  of  differentiation  and 
integration,  which  of  necessity  brings  together,  or  keeps  to- 
gether, like  individuals,  and  separates  unlike  ones  from  them, 
there  must  nevertheless  be  maintained  a  tolerably  uniform 
species  ;  so  long  as  there  continues  a  tolerably  uniform,  set  of 
conditions  in  which  it  may  exist.  But  if  the  conditions 
change,  either  absolutely  by  some  disturbance  of  the  habitat, 
or  relatively  by  spread  of  the  species  into  other  habitats,  then 
the  divergent  individuals  that  result,  must  be  segregated 
by  the  divergent  sets  of  conditions  into  distinct  varieties 
(First  Principles,  §  126).  When,  instead  of  contemplating 
a  species  in  the  aggregate,  we  confine  our  attention  to  a 
single  member  and  its  descendants,  we  see  it  to  be  a  corollary 
from  the  general  law  of  equilibration,  that  the  moving  equili- 


VARIATION.  271 

brium  constituted  by  the  vital  actions  in  each  member  of 
this  family,  must  remain  constant  so  long  as  the  external  ac- 
tions to  which  they  correspond  remain  constant ;  and  that  if 
the  external  actions  are  changed,  the  disturbed  balance  of 
internal  changes,  if  not  overthrown,  cannot  cease  undergoing 
modification  until  the  internal  changes  are  again  in  equili- 
brium with  the  external  actions :  corresponding  structural 
alterations  having  arisen. 

Or  passing  from  these  derivative  laws  to  the  ultimate  law, 
we  see  that  Variation  is  necessitated  by  the  persistence  of  force. 
The  members  of  a  species  inhabiting  any  area,  cannot  be  subject 
to  like  aggregates  of  forces  over  the  whole  of  that  area.  And 
if,  in  different  parts  of  the  area,  different  kinds  or  amounts  or 
combinations  of  forces  act  on  them,  they  cannot  but  become 
different  in  themselves  and  in  their  progeny.  To  say  otherwise, 
is  to  say  that  differences  in  the  forces  will  not  produce  differ- 
ences in  the  effects ;  which  is  to  deny  the  persistence  of  force. 

Whence  it  is  also  manifest,  that  there  can  be  no  variation 
of  structure,  but  what  is  directly  or  indirectly  consequent  on 
variation  of  function.  On  the  one  hand,  organisms  in  com- 
plete equilibrium  with  their  conditions,  cannot  be  changed 
except  by  change  in  their  conditions ;  since,  to  assert  other- 
wise, is  to  assert  that  there  can  be  an  effect  without  a  cause  ; 
which  is  to  deny  the  persistence  of  force.  On  the  other  hand, 
any  change  of  conditions  can  affect  an  organism  only  by 
changing  the  actions  going  on  in  it — only  by  altering  its  func- 
tions. The  alterations  of  functions  being  necessarily  towards 
a  re- establishment  of  the  equilibrium,  (for  if  not,  the  equili- 
brium must  be  destroyed  and  the  life  cease,  either  in  the  in- 
dividual or  in  descendants,)  it  follows  that  the  structural  alter- 
ations directly  caused,  are  adaptations  ;  and  that  the  correlated 
structural  alterations  indirectly  caused,  are  the  concomitants  of 
adaptations.  Hence,  though,  by  the  intercourse  of  organisms 
that  have  been  functionally,  and  structurally  modified  in  dif- 
ferent directions,  there  may  result  organisms  that  deviate  in 
compound  ways  which  appear  unrelated  to  external  condi- 


272  THE    INDUCTIONS    OF    BIOLOGY. 

tions,  the  deviations  of  such  organisms  must  still  be  regarded 
as  indirect  results  of  functional  adaptations.  We  must  say 
that  in  all  cases,  adaptive  change  of  function  is  the  primary 
and  ever-acting  cause  of  that  change  of  structure  which  con- 
stitutes variation ;  and  that  the  variation  which  appears  to 
be  "  spontaneous,"  is  derivative  and  secondary. 


CHAPTER  X. 

GEXESJS,    HEREDITY,    AND    VARIATION. 

$  92.  A  question  raised,  and  hypothetically  answered,  in 
§§  78  and  79,  was  there  postponed  until  we  had  dealt  with  the 
topics  of  Heredity  and  Variation.  Let  us  now  resume  the 
consideration  of  this  question,  in  connexion  with  sundry 
others  which  the  facts  suggest. 

After  contemplating  the  several  methods  by  which  the 
multiplication  of  organisms  is  carried  on  —  after  ranging 
ihem  under  the  two  heads  of  Homogenesis,  in  which  the  suc- 
cessive generations  are  similarly  produced,  and  Heterogenesis, 
in  which  they  are  dissimilarly  produced — after  observing 
that  Homogenesis  is  always  sexual  genesis,  while  Heteroge- 
nesis is  asexual  genesis  with  occasionally-recurring  sexual 
genesis  ;  we  came  to  the  questions — why  is  it  that  some  or- 
ganisms multiply  in  the  one  way,  and  some  in  the  other  ? 
and  why  is  it  that  where  agamogenesis  prevails,  it  is  usually, 
from  time  to  time,  interrupted  by  gamogenesis  ?  In  seeking 
an  answer  to  this  question,  we  inquired  whether  there  are, 
common  to  both  Homogenesis  and  Heterogenesis,  any  condi- 
tions under  which  alone  sperm-cells  and  germ-cells  arise  and 
are  united,  for  the  production  of  new  organisms ;  and  we 
reached  the  conclusion  that,  in  all  cases,  they  arise  only 
when  there  is  an  approach  to  equilibrium  between  the  forces 
which  produce  growth  and  the  forces  which  oppose  growth. 
This  answer  to  the  question — when  does  gamogenesis  recur  i' 


274  THE    INDUCTIONS    OF    BIOLOGY. 

still  left  unanswered  tlie  question — xdiy  does  gamogenetfia 
recur  ?  And  to  this  the  reply  suggested  was,  that  the  ap- 
proach towards  general  equilibrium  in  organisms,  "is  ac- 
companied by  an  approach  towards  molecular  equilibrium  in 
them ;  and  that  the  need  for  this  union  of  spe7'm-cell  and 
germ-cell,  is  the  need  for  overthrowing  this  equilibrium,  and 
re-establishing  active  molecular  change  in  the  detached  germ 
— a  result  which  is  probably  effected  by  mixing  the  slightly- 
different  physiological  units  of  slightly-different  individuals." 
This  is  the  hypothesis  which  we  have  now  to  consider.  Let 
us  first  look  at  the  evidences  which  certain  inorganic  pheno- 
mena furnish. 

The  molecules  of  any  aggregate  which  have  not  a  balanced 
arrangement,  inevitably  tend  towards  a  balanced  arrangement. 
As  before  mentioned  (First  Principles,  §  103)  amorphous 
wrought  iron,  when  subject  to  continuous  jar,  begins  to  arrange 
itself  into  crystals — its  atoms  assume  a  condition  of  polai 
equilibrium.  The  particles  of  unannealed  glass,  which  are  so 
unstably  arranged  that  slight  disturbing  forces  make  them 
separate  into  small  groups,  take  advantage  of  that  greater 
freedom  of  movement  given  by  a  raised  temperature,  to  ad- 
just themselves  into  a  state  of  relative  rest.  During  any 
such  re-arrangement,  the  aggregate  exercises  a  coercive  force 
over  its  units.  Just  as  in  a  growing  crystal,  the  atoms  suc- 
cessively assimilated  from  the  solution,  are  made  by  the  al- 
ready-ciystallized  atoms  to  take  a  certain  form,  and  even  to 
re-complete  that  form  when  it  is  broken  ;  so  in  any  mass  of 
unstably-arranged  atoms  that  passes  into  a  stable  arrangement, 
each  atom  conforms  to  the  forces  exercised  on  it  by  all  the 
other  atoms.  This  is  a  corollary  from  the  general  law  of 
equilibration.  We  saw  (First  Principles,  %  130)  that  every 
change  is  towards  equilibrium ;  and  that  change  can  never 
cease  until  equilibrium  is  reached.  Organisms,  above 

ill  other  aggregates,  conspicuously  display  this  progressive 
equilibration ;  because  their  units  are  of  such  kinds,  and  so 
conditioned,  as   to  admit  of  easy  re-arrangement.      Those 


GENESIS,    HEREDITY,    AND    VARIATION.  275 

extremely  active  changes  which  go  on  during  the  early 
btages  of  evolution,  imply  an  immense  excess  of  the  mole- 
cular forces  over  those  antagonist  forces  which  the  aggregate 
exercises  on  the  molecules.  While  this  excess  continues,  it 
is  expended  in  growth,  development,  and  function — expendi- 
ture for  any  of  these  purposes,  being  proof  that  part  of  the 
force  embodied  in  molecular  tensions,  remaias  unbalanced. 
Eventually,  however,  this  excess  diminishes.  Either,  as  in 
organisms  which  do  not  expend  much  force,  decrease  of  assi- 
milation leads  to  its  decline  ;  or,  as  in  organisms  which  ex- 
pend much  force,  it  is  counterbalanced  by  the  rapidly-increas- 
ing re-actions  of  the  aggregate  (§  46).  The  cessation  of 
growth,  when  followed,  as  in  some  organisms,  by  death,  im- 
plies the  arrival  at  an  equilibrium  between  the  molecular 
forces,  and  those  forces  which  the  aggregate  opposes  to  them. 
When,  as  in  other  organisms,  growth  ends  in  the  establish- 
ment of  a  moving  equilibrium,  there  is  implied  such  a  de- 
creased preponderance  of  the  molecular  forces,  as  leaves  no 
surplus  beyond  that  which  is  used  up  in  functions.  The  de- 
clining functional  activity,  characteristic  of  advancing  life, 
expresses  a  further  decline  in  this  surplus.  And  when  all 
vital  movements  come  to  an  end,  the  implication  is,  that 
the  actions  of  the  units  on  the  aggregate  and  the  re- 
actions  of  the  aggregate  on  the  units,  are  completely  bal- 
anced. Hence,  while  a  state  of  rapid  growth  indi- 
cates such  a  play  of  forces  among  the  units  of  an  aggregate, 
as  will  produce  active  re-distribution ;  tha  diminution  and 
arrest  of  growth,  shows  that  the  units  have  fallen  into  such 
relative  positions  that  re-distribution  is  no  longer  so  facile. 
When,  therefore,  we  see  that  gamogenesis  recurs  only  when 
growth  is  decreasing,  or  has  come  to  an  end,  we  must  say 
that  it  recurs  only  when  the  organic  units  are  approxima- 
ting to  equilibrium — only  when  their  mutual  restraints  pre- 
vent them  from  readily  changing  their  arrangements  in  obe- 
dience to  incident  forces. 

That  units  of  like  forms  can  be  built  up  into  a  more  stabU' 


276  THE    INDUCTIONS    OF    BIOLOGY. 

aggregate  than  units  of  slightly  unlike  forms,  is  tolerably 
manifest,  a, priori.  And  we  have  facts  which  prove  that  mixing 
allied  but  somewhat  different  units,  docs  lead  to  comparative  in- 
stability. Most  metallic  alloys  exemplify  this  truth.  Com- 
mon solder,  which  is  a  mixture  of  lead  and  tin,  melts  at  a  much 
lower  temperature  than  either  lead  or  tin.  The  compound  of 
lead,  tin,  and  bismuth,  called  "  fusible  metal,"  becomes  fluid 
at  the  temperature  of  boiling  water ;  while  the  temperatures 
at  which  lead,  tin,  and  bismuth  become  fluid,  are,  respectively, 
G12°,  442°,  and  497°,  F.  Still  more  remarkable  is  the  illustra- 
tion furnished  by  potassium  and  sodium.  These  metals  are 
very  near  akin  in  all  respects — in  their  specific  gravities,  their 
atomic  weights,  their  chemical  affinities,  and  the  properties 
of  their  compounds.  That  is  to  say,  all  the  evidences  unite  to 
shosv  that  their  units,  though  not  identical,  have  a  close  resem- 
blance. What  now  happens  when  the}'  are  mixed  ?  Potassium 
alone  melts  at  136°,  sodium  alone  melts  at  190°,  but  the  alloy  of 
potassium  and  sodium,  is  liquid  at  the  ordinary  temperature  of 
the  air.  Observe  the  meaning  of  these  facts,  expressed  in 
general  terms.  The  maintenance  of  a  solid  form  by  any  group 
of  units,  implies  among  them  an  arrangement  so  stable,  that 
it  cannot  be  overthrown  by  the  incident  forces.  Whereas  the 
assumption  of  a  liquid  form,  implies  that  the  incident  forces 
suffice  to  destroy  the  arrangement  of  the  units.  In  the  one 
case,  the  thermal  undulations  fail  to  dislocate  the  parts  ;  while 
in  the  other  case,  the  parts  are  so  dislocated  by  the  thermal 
undulations,  that  they  fall  into  total  disorder — a  disorder 
admitting  of  easy  re-arrangement  into  any  other  order.  For 
the  liquid  state  is  a  state  in  which  the  units  become  so  far  free 
from  mutual  restraints,  that  incident  forces  can  change  their 
relative  positions  very  readily.  Thus  we  have  reason  to 
conclude,  that  an  aggregate  of  units  which,  though  in  the 
main  similar  to  each  other,  have  minor  differences,  must  be 
more  unstable  than  an  aggregate  of  homogeneous  units :  the 
one  will  yield  to  disturbing  forces  which  the  other  successfully 
resists. 


GENESIS,    HEREDITY,    AND    VARIATION.  277 

Now  though  the  colloidal  atoms  of  which  organisms  are 
mainly  built,  are  themselves  highly  composite  ;  and  though 
the  ph}-siological  units  compounded  out  of  these  colloidal 
atoms,  must  have  structures  far  more  involved  ;  yet  it  must 
happen  with  such  units,  as  with  simple  units,  that  those 
which  have  exactl}r  like  forms,  will  admit  of  arrangement  into 
a  more  stable  aggregate  than  those  which  have  slightly- 
unlike  forms.  Among  units  of  this  order,  as  among  units 
of  a  simpler  order,  imperfect  similarity  must  entail  imperfect 
polar  balance,  and  consequent  diminished  ability  to  withstand 
disturbing  forces.  Hence,  given  two  organisms  which,  by 
diminished  nutrition  or  increased  expenditure,  are  being  ar- 
rested in  their  growths — given  in  each  an  approaching 
equilibrium  between  the  forces  of  the  units  and  the  forces  of 
the  aggregate — given,  that  is,  such  a  comparatively-balanced 
state  among  the  units,  that  re- arrangement  of  them  by  inci- 
dent forces  is  no  longer  so  easy  ;  and  it  will  follow  that  by 
imiting  a  group  of  units  from  the  one  organism  with  a  group 
of  slightly-different  units  from  the  other,  the  tendency  to- 
wards equilibrium  will  be  diminished,  and  the  mixed  units 
will  be  rendered  more  modifiable  in  their  arrangements  by 
the  forces  acting  on  them  :  they  will  be  so  far  freed  as  to  be- 
come again  capable  of  that  re-distribution  which  constitutes 
evolution.  This  view  of  the  matter  is  in  harmony 

with  the  results  of  observation  on  the  initial  stages  of  develop- 
ment. Some  pages  back,  it  was  asserted  that  sperm-cell  and 
germ-cell  severally  arrive,  before  their  union,  at  a  condition 
of  equilibrium.  Though  approximately  true,  this  is  not  liter- 
ally true.  I  learn  from  Dr  "W.  II.  Ransom,  who  has  investi- 
gated the  question  with  great  care,  that  the  unfertilized  ovum 
continues,  for  a  time,  to  undergo  changes  similar  to  those  which 
the  fertilized  ovum  undergoes;  butthat  these  changes,  becoming 
languid  and  incomplete,  are  finally  arrested  by  decomposition. 
Here  we  find  what  might  be  expected.  In  the  first  place,  an 
organism  which  develops  germ-cells,  is  not  in  a  state  of  mole- 
cular equilibrium,  but  in  a  state  of  approach  to  such  cquili- 


278  THE    INDUCTIONS    OF    BIOLOGY. 

brmm.  Hence,  a  group  of  physiological  units  cast  off  from  it, 
will  not  be  wholly  without  a  tendency  to  undergo  the  struc- 
tural re-arrangements  which  we  call  development ;  but  will 
have  this  tendency  unduly  restrained  by  partially-balanced 
polarities.  In  the  second  place,  undue  restraint  of  the  phy- 
siological units,  while  it  renders  them  as  wholes  less-easil)r 
altered  in  their  relative  positions  by  incident  forces,  thereby 
also  renders  them  more  liable  to  be  individually  decomposed 
by  incident  forces  :  the  same  thermal  undulations  which,  if 
the  physiological  units  are  comparatively  free,  will  aid  their 
re-arrangement  by  giving  them  still  greater  freedom,  will,  if 
they  are  comparatively  fixed,  begin  to  change  the  arrange- 
ments of  their  components — will  decompose  them.  In  the 
third  place,  their  decomposition  will  be  prevented  as  well  as 
their  re-distribution  facilitated,  by  such  disturbance  of  their 
polarities  as  we  have  seen  must  result  from  mixing  with  them 
the  slightly-unlike  units  of  another  organism. 

And  now  let  us  test  this  hypothesis,  by  seeing  what  power 
it  gives  us  of  interpreting  established  inductions. 

§  93.  The  majority  of  plants  being  hermaphrodites,  it  has, 
until  quite  recently,  been  supposed  that  the  ovules  of  each 
flower  are  fertilized  by  pollen  from  the  anthers  of  the  same 
flower.  Mr  Darwin,  however,  has  shown  that  the  arrange- 
ments are  generally  such  as  to  prevent  this  :  either  the  ovules 
and  the  pollen  are  not  ripe  simultaneously,  or  obstacles  pre- 
vent access  of  the  one  to  the  other.  At  the  same  time,  he  has 
shown  that  there  exist  arrangements,  often  of  a  remarkable 
kind,  which  facilitate  the  transfer  of  pollen  by  insects  from  the 
stamens  of  one  flower  to  the  pistil  of  another.  Simi- 

larly, it  has  been  found  that  among  the  lower  animals,  herraa- 
phrodism  does  not  usually  involve  the  production  of  fertile 
germs,  by  the  union  of  sperm-cells  and  germ-cells  developed 
in  the  same  individual ;  but  that  the  reproductive  centres  of 
one  individual  are  united  with  those  of  another,  to  produce 
fertile  germs.    Either,  as  in  the  Pyrosoma,  the  Perophora,  and 


GENESIS,    HEREDITY,    AND    VARIATION.  279 

in  mnnv  higher  molluscs,  the  ova  an  J  spermatozoa  are  ma- 
fared  at  different  times ;  or,  as  in  annelids,  they  are  prevented 
by  their  relative  positions  from  coining  in  contact. 

Remembering  the  fact  that  among  the  higher  classes  of 
organisms,  fertilization  is  always  effected  by  combining  the 
sperm-cell  of  one  individual  with  the  germ-cell  of  another ; 
and  joining  with  it  the  fact  that  among  hermaphrodite  organ- 
isms, the  germ-cells  developed  in  any  individual,  are  usually 
not  fertilized  by  sperm-cells  developed  in  the  same  individual ; 
we  see  reason  for  thinking  that  the  essential  thing  in  fertiliz- 
ation, is  the  union  of  specially-fitted  portions  of  different  or- 
ganisms. If  fertilization  depended  on  the  peculiar  pi'operties 
of  sperm-cell  and  germ-cell,  as  such  ;  then,  in  hermaphrodite 
organisms,  it  would  be  a  matter  of  indifference  whether  the 
united  sperm-cells  and  germ-cells  were  those  of  the  same  in- 
dividual, or  those  of  different  individuals.  But  the  circum- 
stance that  there  exist  in  such  organisms,  elaborate  ap- 
pliances for  mutual  fertilization,  shows  that  unlikeness  of 
derivation  in  the  united  reproductive  centres,  is  the  deside- 
ratum. Now  this  is  just  what  the  foregoing  hj'pothesis 
implies.  If,  as  was  concluded,  fertilization  has  for  its  object 
the  disturbance  of  that  approximate  equilibrium  existing 
among  the  physiological  units  separated  from  an  adult  organ- 
ism ;  and  if,  as  we  saw  reason  to  think,  this  object  is  effected 
by  mixture  with  the  slightly-different  physiological  units  of 
another  organism  ;  then,  we  at  the  same  time  see  reason  to 
think,  that  this  object  will  not  be  effected  by  mixture  with 
physiological  units  belonging  to  the  same  organism.  Thus, 
the  hypothesis  leads  us  to  expect  such  provisions  as  we  find 
?xist. 

§  94.  But  here  a  difficulty  presents  itself.  These  proposi- 
tions seem  to  involve  the  conclusion,  that  self-fertilization  is 
impossible.  It  apparently  follows  from  them,  that  a  group  of 
physiological  units  from  one  part  of  an  organism,  ought  to 
have  no  power  of  altering  the  state  of  approaching  balance  in 


280  THE   INDUCTIONS    OF    BIOLOGY. 

a  group  from  another  part  of  it.  Yet  self-fertilization  does 
occur.  Though  the  ovules  of  one  plant,  are  generally  fer- 
tilized by  pollen  from  another  plant  of  the  same  kind ;  yet 
they  may  be,  some  of  them,  fertilized  by  the  pollen  of  the  same 
plant.  And  though,  among  hermaphrodite  animals,  self-fer- 
tilization is  usually  negatived  by  structural  or  functional  ar- 
rangements ;  yet  in  certain  Entozoa,  there  appear  to  be  special 
provisions  by  which  the  sperm-cells  and  germ-cells  of  the  same 
individual  may  be  united,  when  not  previously  united  with 
those  of  another  individual.  Certainly,  at  first  sight,  these 
facts  do  not  consist  with  the  above  supposition.  Neverthe- 
less, there  is  a  satisfactory  solution  of  them. 

In  the  last  chapter,  when  considering  the  variations  that 
may  result  in  offspring  from  the  combination  of  unlike 
parental  constitutions,  it  was  pointed  out  that  in  an  unfolding 
organism,  composed  of  slightly-different  physiological  units 
derived  from  slightly-different  parents,  there  cannot  be  main- 
tained an  even  distribution  of  the  two  orders  of  units.  We 
saw  that  the  instability  of  the  homogeneous,  negatives  the 
uniform  blending  of  them  ;  and  that,  by  the  process  of  differ- 
entiation and  integration,  they  must  be  more  or  less  separated  ; 
so  that  in  one  part  of  the  body  the  influence  of  one  pai'ent  will 
predominate,  and  in  another  part  of  the  body  the  influence  of 
the  other  parent :  an  inference  which  harmonizes  with  daily 
observation.  And  we  also  saw,  that  the  sperm-cells  or  germ- 
.  cells  produced  by  such  an  organism,  must,  in  virtue  of  these 
same  laws,  be  more  or  less  unlike  one  another.  It  was  shown 
that  through  segregation,  some  01  t,ne  sperm-cells  or  germ- 
cells  will  get  an  excess  of  the  physiological  units  derived 
from  one  side,  and  some  of  them  an  excess  of  those  derived 
from  the  other  side :  a  cause  which  accounts  for  the  unlikenesses 
among  offspring  simultaneously  produced.  Now  from  this 
segregation  of  the  different  orders  of  physiological  units,  in- 
herited from  different  parents  and  lines  of  ancestry,  there 
arises  the  possibility  of  self-fertilization  in  hermaphrodite 
organisms.     If  the  physiological  units  contained  in  the  sperm- 


GENESIS,    HEREDITY,    AND    VARIATION.  281 

colls  and  germ-cells  of  the  same  flower,  are  not  quite  homo- 
geneous— if  in  some  of  the  ovules  the  physiological  units 
derived  from  the  one  parent  greatly  predominate,  and  in  some 
of  the  ovules  those  derived  from  the  other  parent ;  and  if  the 
like  is  true  of  the  pollen-cells  ;  then,  some  of  the  ovules  may 
be  nearly  as  much  contrasted  with  some  of  the  pollen-cells,  in 
Ihe  characters  of  their  contained  units,  as  were  the  ovules  and 
pollen-cells  of  the  parents  from  which  the  plant  proceeded. 
Jietween  part  of  the  sperm-cells  and  part  of  the  germ-cells,  the 
community  of  nature  will  be  such  that  fertilization  will  not 
result  from  their  union  ;  but  between  some  of  them,  the 
differences  of  constitution  will  be  such  that  their  union 
will  produce  the  requisite  molecular  instability.  The  facts, 
so  far  as  they  are  known,  seem  in  harmony  with  this  deduction. 
Self-fertilization  in  flowers,  when  it  takes  place,  is  not  so 
efficient  as  mutual  fertilization.  Though  some  of  the  ovules 
produce  seeds,  yet  more  of  them  than  usual  are  abortive. 
From  which,  indeed,  results  the  establishment  of  varieties  that 
have  structures  favourable  to  mutual  fertilization;  since,  being 
more  prolific,  these  have,  other  things  equal,  greater  chances 
in  the  "  struggle  for  existence." 

Further  evidence  is  at  hand  in  support  of  this  interpreta- 
tion. There  is  reason  to  believe  that  self-fertilization,  which 
at  the  best  is  comparatively  inefficient,  loses  all  efficiency  in 
course  of  time.  After  giving  an  account  of  the  provisions  for 
an  occasional,  or  a  frequent,  or  a  constant  crossing  between 
flowers  ;  and  after  quoting  Prof.  Huxley  to  the  effect  that 
among  hermaphrodite  animals,  there  is  no  case  in  which  "  tbo 
occasional  influence  of  a  distinct  individual  can  be  shown  to 
be  physically  impossible  ;  "  Mr  Darwin  writes — "  from  these 
several  considerations  and  from  the  many  special  facts  which 
I  have  collected,  but  which  I  am  not  here  able  to  give,  I  am 
strongly  inclined  to  suspect  that,  both  in  the  vegetable  and 
animal  kingdoms,  an  occasional  intercross  with  a  distinct  in- 
dividual is  a  law  of  nature.  *  *  *  in  none,  as  I  suspect, 
can  self-fertilization  go  on  for  perpetuity."  This  conclusion, 
19 


282  THE    INDUCTIONS    OF    BIOLOGY. 

based  wholly  on  observed  facts,  is  just  the  conclusion  to  -which 
the  foregoing  argument  points.  That  necessary  action  and 
the  re-action  between  the  parts  of  an  organism  and  the 
organism  as  a  whole — that  power  of  the  aggregate  to  re-mould 
tiie  units,  which  is  the  correlative  of  the  power  of  the  units  to 
build  up  into  such  an  aggregate  ;  implies  that  any  differences 
existing  between  the  units  inherited  by  an  organism,  must 
gradually  diminish.  Being  subject  in  common  to  the  total 
lorces  of  the  organism,  they  will  in  common  be  modified  to- 
wards congruity  with  these  forces;  and  therefore  towards 
likeness  with  each  other.  If,  then,  in  a  self- fertilizing  organism 
and  its  self-fertilizing  descendants,  such  contrasts  as  origin- 
ally existed  among  the  physiological  units,  are  progressive- 
ly obliterated  —  if,  consequently,  there  can  no  longer  be  a 
segregation  of  different  physiological  units  in  different  sperm- 
cells  and  germ-cells  ;  self-fertilization  will  become  impossible  : 
step  by  step  the  feitility  will  diminish,  and  the  series  will 
finally  die  out. 

And  now  observe,  in  confirmation  of  this  view,  that  self- 
fertilization  is  limited  to  organisms  in  which  an  approximate 
equilibrium  among  the  organic  forces,  is  not  long  maintained. 
While  growth  is  actively  going  on,  and  the  physiological  units 
are  subject  to  a  continually-changing  distribution  of  forces, 
no  decided  assimilation  of  the  units  can  be  expected  :  like 
forces  acting  on  the  unlike  units,  will  tend  to  segregate  them, 
so  long  as  continuance  of  evolution  permits  further  segrega- 
tion ;  and  only  when  further  segregation  cannot  go  on,  will 
the  like  forces  tend  to  assimilate  the  units.  Hence,  where 
there  is  no  prolonged  maintenance  of  an  approximate  organic 
balance,  self-fertilization  may  be  possible  for  some  gener- 
ations ;  but  it  will  be  impossible  in  organisms  distinguished 
by  a  sustained  moving  equilibrium. 

§  95.  The  interpretation  which  it  affords  of  sundry  pheno- 
mena familiar  to  breeders  of  animais,  adds  probability  to  the 
hypothesis.    Mr  Darwin  has  collected  a  large  "  body  of  facte, 


GENESIS,    HEREDITY,    AXP    VARIATION.  283 

showing,  in  accordance  with  the  almost  universal  belief  ol 
breeders,  that  with  animals  and  plants  a  cross  between  different 
varieties,  or  between  individuals  of  the  same  variety  but  ot 
another  strain,  gives  vigour  and  fertility  to  the  offspring ;  and 
on  the  other  hand,  that  close  interbreeding  diminishes  vigour 
and  fertility," — a  conclusion  harmonizing  with  the  current 
belief  respecting  family-intermarriages  in  the  human  race. 
Have  we  not  here  a  solution  of  these  facts  ?  Relations  must,  on 
the  average  of  cases,  be  individuals  whose  physiological  units 
are  more  nearly  alike  than  usual.  Animals  of  different 
varieties  must  be  those  whose  physiological  units  are  more 
unlike  than  usual.  In  the  one  case,  the  unlikeness  of  the 
units  may  frequently  be  insufficient  to  produce  fertilization  ; 
or,  if  sufficient  to  produce  fertilization,  not  sufficient  to  produce 
that  active  molecular  change  required  for  vigorous  develop- 
ment. In  the  other  case,  both  fertilization  and  vigorous 
development  will  be  made  probable. 

Nor  are  we  without  a  cause  for  theirregular  manifestation  ot 
these  general  tendencies.  The  mixed  physiological  units  com- 
posing any  organism,  being,  as  we  have  seen,  more  or  less  se- 
gregated in  the  reproductive  centres  it  throws  off;  there  may 
arise  various  results,  according  to  the  degrees  of  difference 
among  the  units,  and  the  degrees  in  which  the  units  are  segre- 
gated. Of  two  cousins  who  have  married,  the  common  grand- 
parents may  have  had  either  similar  or  dissimilar  constitu- 
tions; and  if  their  constitutions  were  dissimilar,  the  probability 
that  their  married  grandchildren  will  have  offspring  will  be 
greater  than  if  their  constitutions  were  similar.  Or  the 
brothers  and  sisters  from  whom  these  cousins  descended,  in- 
stead of  severally  inheriting  the  constitutions  of  their  parents 
in  tolerably  equal  degrees,  may  have  severally  inherited  them 
in  very  different  degrees  :  in  which  last  case,  intermarriages 
among  the  grandchildren  will  be  less  likely  to  prova  infertile. 
Or  the  brothers  and  sisters  from  whom  these  cousins  de- 
scended, may  severally  have  married  persons  very  like,  or 
very  unlike,  themselves  ;    and  from  this  cause    there   may 


284  THE    INDUCTIONS   OF    BIOLOGY. 

have  resulted,  either  an  undue  likeness,  or  a  due  unlike- 
ness,  between  the  married  cousins.  These  several  causes, 
conspiring  and  conflicting  in  endless  ways  and  degrees,  will 
work  multiform  effects.  Moreover,  differences  of  segrega- 
tion will  make  the  reproductive  centres  produced  by  the 
same  nearly-related  organisms,  vary  considerably  in  their 
amounts  of  unlikeness ;  and  therefore,  supposing  their  amounts 
of  unlikeness  great  enough  to  cause  fertilization,  this  fertiliza- 
tion will  be  effective  in  various  degrees.  Hence  it  may  happen 
that  among  offspring  of  nearly-related  parents,  there  may  be 
some  in  which  the  want  of  vigour  is  not  marked,  and  others  in 
which  there  is  decided  want  of  vigour.  So  that  we  are  alike 
shown  why  in-and-in  breeding  tends  to  diminish  both  fertility 
and  vigour ;  and  why  the  effect  cannot  be  a  uniform  effect,  but 
only  an  average  effect. 

§  96.  While,  if  the  foregoing  arguments  are  valid,  gamo- 
genesis  has  for  its  main  end,  the  initiation  of  a  new  develop- 
ment by  the  overthrowof  that  approximate  equilibrium  arrived 
at  among  the  molecules  of  the  parent-organisms ;  a  further  end 
appears  to  be  subserved  by  it.  Those  inferior  organisms 
which  habitually  multiply  by  agamogenesis,  have  conditions 
of  life  that  are  simple  and  uniform  ;  while  those  organisms 
that  have  highly-complex  and  variable  conditions  of  life, 
habitually  multiply  by  gamogenesis.  Now  if  a  species  has 
complex  and  variable  conditions  of  life,  its  members  must  be 
severally  exposed  to  sets  of  conditions  that  are  slightly 
different :  the  aggregates  of  incident  forces  cannot  be  alike 
for  all  the  scattered  individuals.  Hence,  as  functional 
deviation  must  ever  be  inducing  structural  deviation,  each 
individual  throughout  the  area  occupied,  tends  to  become 
fitted  for  the  particular  habits  which  its  particular  conditions 
necessitate  ;  and  in  so  far,  emfitted  for  the  average  habits 
proper  to  the  species.  But  these  undue  specializations  are 
continually  checked  by  gamogenesis.  As  Mr  Darwin  remarks 
— "  intercrossing  plays  a  very  important  part  in  nature  in 


GENESIS,    HEREDITY,    AND   VARIATION.  285 

keeping  the  individuals  of  the  same  species,  or  of  the  variety, 
true  and  uniform  in  character :"  the  idiosyncratic  divergence 
obliterate  each  other.  Gamogenesis,  then,  is  a  means  of 
turning  to  positive  advantage,  the  individual  differentiations 
which,  in  its  absence,  would  result  in  positive  disadvantage. 
Were  it  not  that  individuals  are  ever  being  made  unlike  each 
other  by  their  unlike  conditions,  there  would  not  arise  among 
them  those  contrasts  of  molecular  constitution,  which  we  have 
seen  to  be  needful  for  producing  the  fertilized  germs  of  new 
individuals.  And  were  not  these  individual  differentiations 
ever  being  mutually  cancelled,  they  would  end  in  a  fatal 
narrowness  of  adaptation. 

This  truth  will  be  most  clearly  seen  if  we  reduce  it  to  its 
purely  abstract  form,  thus : — Suppose  a  quite  homogeneous 
species,  placed  in  quite  homogeneous  conditions  ;  and  suppose 
the  constitutions  of  all  its  members  in  complete  concord  with 
their  absolutely-uniform  and  constant  conditions;  what  must 
happen  ?  The  species,  individually  and  collectively,  is  in  a 
state  of  perfect  moving  equilibrium.  All  disturbing  forces 
have  been  eliminated.  There  remains  no  force  which  can,  in 
any  way,  change  the  state  of  this  moving  equilibrium  ;  either 
in  the  species  as  a  whole  or  in  its  members.  But  we  have 
seen  (First  Principles,  §  133)  that  a  moving  equilibrium  is  but. 
a  transition  towards  complete  equilibration,  or  death.  The 
absence  of  differential  or  un-equilibrated.  forces  among  the 
members  of  a  species,  is  the  absence  of  all  forces  that  can 
cause  changes  in  the  conditions  of  its  members — is  the  ab- 
sence of  all  forces  which  can  initiate  new  organisms.  To  sav, 
as  above,  that  complete  molecular  homogeneity  existing 
among  the  members  of  a  species,  must  render  impossible  that 
mutual  molecular  disturbance  which  constitutes  fertilization, 
is  but  another  way  of  saying,  that  the  actions  and  re-actions 
of  each  organism,  being  in  perfect  balance  with  the  actions 
and  re-actions  of  the  environment  upon  it,  there  remains  in 
each  organism,  no  force  by  which  it  differs  from  any  other 
— no  force  which   any  other  does  not  meet  with  an  exactly 


286 


THE   INDUCTIONS   Of    BIOLOGY. 


equal    force — no  force  which    can  set  up  a   new   evo'ution 
among  the  units  of  any  other. 

And  so  we  reach  the  remarkable  conclusion,  that  the  life  of 
a  species,  like  the  life  of  an  individual,  is  maintained  by  tho 
unequal  and  ever- varying  actions  of  incident  forces  on  its 
different  parts.  An  individual  homogeneous  throughout,  and 
having  its  substance  everywhere  continuously  subject  to  like 
actions,  could  undergo  none  of  those  changes  which  life  con- 
sists of;  and  similarly,  an  absolutely- uniform  species,  having  all 
its  members  exposed  to  identical  influences,  would  be  deprived 
of  that  initiator  of  change  which  maintains  its  existence  as 
a  species.  Just  as,  in  each  organism,  incident  forces  constantly 
produce  divergences  from  the  mean  state  in  various  directions, 
which  are  constantly  balanced  by  opposite  divergences  indi- 
rectly produced  by  other  incident  forces ;  and  just  as  the 
combination  of  rhythmical  functions  thus  maintained,  consti- 
tutes the  life  of  the  organism  ;  so,  in  a  species,  there  is,  through 
gamogenesis,  a  perpetual  neutralization  of  those  contrary  de- 
viations from  the  mean  state,  which  are  caused  in  its  different 
parts  by  different  sets  of  incident  forces  ;  and  it  is  similarly 
by  the  rhythmical  production  and  compensation  of  these  con- 
trary deviations,  that  the  species  continues  to  live.  The 
moving  equilibrium  in  a  species,  like  the  moving  equilibrium 
in  an  individual,  would  rapidly  end  in  complete  equilibration, 
or  death,  were  not  its  continually- dissipated  forces  continually 
re-supplied  from  without.  Besides  owing  to  the  external 
world,  those  energies  which,  from  moment  to  moment,  keep 
up  the  lives  of  its  individual  members ;  every  species  owes 
to  certain  more  indirect  actions  of  the  external  world,  those 
energies  which  enable  it  to  perpetuate  itself  in  successive 
generations. 

§  97.  What  evidence  still  remains,  may  be  conveniently 
woven  up  along  with  a  recapitulation  of  the  argument  pursued 
through  the  last  three  chapters.  Let  us  contemplate  the  facts 
in  their  synthetic  order. 


GENESIS,    HEREDITY,    AND    VARIATION.  287 

Tnat  compounding  and  re-compounding  through  which  we 
pass  from  the  simplest  inorganic  substances  to  the  most  cora» 
plex  organic  substances,  has  several  concomitants.  Each 
Buccessi  ve  stage  of  composition,  presents  us  with  atoms  that  are 
severally  larger  or  more  integrated,  that  are  severally  more 
heterogeneous,  that  are  severally  more  unstable,  and  that  are 
more  numerous  in  their  kinds  (First  Principles,  §  111).  And 
when  we  come  to  the  substances  of  which  living  bodies  are 
formed,  we  find  ourselves  among  multiplied,  divergent  groups 
and  sub-groups  of  compounds,  the  units  of  which  are  large, 
heterogeneous,  and  unstable,  in  high  degrees.  There  is  no 
reason  to  assume  that  this  process  ends  with  the  formation  of 
those  complex  colloids  which  characterize  organic  matter.  A 
more  probable  assumption  is,  that  out  of  the  complex  colloidal 
atoms,  there  are  evolved,  by  a  still  further  integration,  atoms 
that  are  still  more  heterogeneous,  and  of  kinds  that  are  still 
more  multitudinous.  What  must  be  their  properties  ?  Al- 
ready the  colloidal  atoms  are  extremely  unstable — capable 
of  being  variously  modified  in  their  characters  by  very  slight 
incident  forces  ;  and  already  the  complexity  of  their  polarities 
prevents  them  from  readily  falling  into  those  positions  of 
polar  equilibrium  which  result  in  crystallization.  Now  the 
organic  atoms  composed  of  these  colloidal  atoms,  must  be  simi- 
larly characterized  in  far  higher  degrees.  Far  more  numerous 
must  be  the  minute  changes  that  can  be  wrought  in  them  by 
minute  external  forces  ;  far  more  free  must  they  remain  for  a 
long  time  to  obey  forces  tending  to  re-distribute  them  ;  and 
far  greater  must  be  the  number  of  their  kinds. 

Setting  out  with  these  physiological  units,  the  existence  of 
which  various  organic  phenomena  compel  us  to  recognize,  and 
the  production  of  which  the  general  law  of  Evolution  thus 
leads  us  to  anticipate  ;  we  get  an  insight  into  the  phenomena 
of  Genesis,  Heredity,  and  Variation.  If  each  organism  is  built 
of  certain  of  these  highly-plastic  units  peculiar  to  its  species 
— units  which  slowly  work  towards  an  equilibrium  of  their 
complex  polarities,  in  producing  an  aggregate  of  the  specific 


288  THE    INDUCTIONS    OF    BIOLOGY. 

structure,  and  which  are  at  the  same  time  slowly  modifiable 
by  the  re-actions  of  this  aggregate — we  see  why  the  mul- 
tiplication of  organisms  proceeds  in  the  several  ways,  and 
with  the  various  results,  which  naturalists  have  observed. 

Heredity,  as  shown  not  only  in  the  repetition  of  the  specific 
structure,  but  in  the  repetition  of  ancestral  deviations  from  it, 
becomes  a  matter  of  course  ;  and  it  falls  into  unison  with  the 
fact  that,  in  various  simple  organisms,  lost  parts  can  be  re- 
placed, and  that,  in  still  simpler  organisms,  a  fragment  can 
develop  into  a  whole. 

While  an  aggregate  of  physiological  units  continues  to 
grow,  by  the  assimilation  of  matter  which  it  moulds  into 
other  units  of  like  type  ;  and  while  it  continues  to  undergo 
changes  of  structure  ;  no  equilibrium  can  be  arrived  at  between 
the  whole  and  its  parts.  Under  these  conditions,  then,  an 
un-differentiated  portion  of  the  aggregate — a  group  of  phy- 
siological units  not  bound  up  into  a  specialized  tissue — will 
be  able  to  arrange  itself  into  the  structure  peculiar  to  the 
species ;  and  will  so  arrange  itself,  if  freed  from  controlling 
forces,  and  placed  in  fit  conditions  of  nutrition  and  temper- 
ature. Hence  the  continuance  of  agamogenesis  in  little- differ- 
entiated organisms,  so  long  as  assimilation  continues  to  be 
greatly  in  excess  of  expenditure. 

But  let  growth  be  checked  and  development  approach  its 
completion — let  the  units  of  the  aggregate  be  severally  exposed 
to  an  almost  constant  distribution  of  forces  ;  and  they  must 
begin  to  equilibrate  themselves.  Arranged  as  they  will 
gradually  be,  into  comparatively  stable  attitudes  in  relation 
to  each  other,  their  mobility  will  diminish  ;  and  groups  of 
them,  partially  or  wholly  detached,  will  no  longer  readily  re- 
arrange themselves  into  the  specific  form.  Agamogenesis  will 
be  no  longer  possible ;  or,  if  possible,  will  be  no  longer  easy. 
When  we  remember  that  the  force  which  keeps  the  Earth 
in  its  orbit,  is  the  gravitation  of  each  particle  in  the  Earth 
towards  every  one  of  the  group  of  particles  existing  91,000,000 
of  miles  off;  we  cannot  reasonably  doubt,  that  each  unit  in 


GENESIS,    HEREDITY,    AND   VARIATION.  289 

an  organism,  acts,  by  its  polar  forces,  on  all  the  other  units, 
and  is  re-acted  on  by  them.  When,  too,  we  learn  that 
glass  has  its  molecular  constitution  changed  by  light,  and 
that  substances  so  rigid  and  stable  as  metals,  have  their 
atoms  re-arranged  by  forces  radiated  in  the  dark  from 
adjacent  objects  ;  we  are  obliged  to  conclude  that  the  ex- 
cessively-unstable units  of  which  organisms  are  built,  must  be 
sensitive  in  a  transcendant  degree,  to  all  the  forces  pervading 
the  organisms  composed  of  them — must  be  tending  ever  to 
re-adjust,  not  only  their  relative  positions,  but  their  molecular 
structures,  into  equilibrium,  with  these  forces.  Hence,  if  ag- 
gregates of  the  same  species  are  differently  conditioned,  and 
re-act  differently  on  their  component  units,  their  component 
units  will  be  rendered  somewhat  different ;  and  they  will 
become  the  more  different  the  more  widely  the  re  •actions 
of  the  aggregates  upon  them  differ,  and  the  greater  the  num- 
ber of  generations  through  which  these  different  re-actions  of 
the  aggregates  upon  them  are  continued. 

If,  then,  unlikenesses  of  function  among  individuals  of  the 
same  species,  produce  unlikenesses  between  the  physiological 
units  of  one  individual  and  those  of  another  ;  it  becomes  com 
prehensible  that  when  groups  of  units  derived  from  two  indi 
viduals  are  united,  the  group  formed  will  be  more  unstable 
than  either  of  the  groups  was  before  their  union :  the  mixed 
units  will  be  less  able  to  resist  those  re-distributing  forces 
which  cause  evolution ;  and  may  so  have  restored  to  them, 
the  capacity  for  development  which  they  had  lost. 

This  view  harmonizes  with  the  conclusion  which  we  saw 
reason  to  draw,  that  fertilization  does  not  depend  on  any 
intrinsic  peculiarities  of  sperm-cells  and  germ-cells  ;  but 
depends  on  their  derivation  from  different  individuals.  It 
explains  the  fact  that  nearly -related  individuals  are  less 
likely  to  have  offspring  than  others ;  and  that  their  offspring, 
when  they  have  them,  are  frequently  feeble.  And  it  gives 
us  a  key  to  the  converse  fact,  that  the  crossing  of  varieties 
results  in  unusual  fertility  and  vigour. 


290  THE    INDUCTIONS   OF    BIOLOGY. 

Bearing-  in  mind  that  the  slightly-different  orders  of  phy- 
siological units  which  an  organism  inherits  from  its  parents, 
are  subject  to  the  same  set  of  forces  ;  and  that  when  the 
organism  is  fully  developed,  this  set  of  forces,  becoming  con- 
stant, tends  slowly  to  re-mould  the  two  orders  of  units  into 
the  same  form  ;  we  see  how  it  happens  that  self-fertilization 
becomes  impossible  in  the  higher  organisms,  while  it  remains 
possible  in  the  lower  organisms.  In  long-lived  creatures  that 
have  tolerably-definite  limits  of  growth,  this  assimilation  of 
the  somewhat-unlike  physiological  units,  is  liable  to  go  on  to 
an  appreciable  extent ;  whereas  _in  organisms  which  do  not 
continuously  subject  their  component  units  to  constant  forces, 
there  will  be  much  less  of  this  assimilation.  And  where  the 
assimilation  is  not  considerable,  the  segregation  of  mixed 
units,  may  cause  the  sperm-cells  and  germ-cells  developed  in 
the  same  individual,  to  be  sufficiently  different  to  produce,  by 
their  union,  fertile  germs  ;  and  several  generations  of  self- 
fertilizing  descendants  may  succeed  one  another,  before  the 
two  orders  of  units  have  had  their  unlikenesses  so  far  diminish- 
ed, that  they  will  no  longer  do  this.  The  same  principles 
explain  for  us  the  variable  results  of  union  between  nearly- 
related  organisms.  According  to  the  contrasts  among  the 
physiological  units  they  inherit  from  parents  and  ancestors  ; 
according  to  the  unlike  proportions  of  the  contrasted  units 
which  they  severally  inherit ;  and  according  to  the  degrees 
of  segregation  of  such  units  in  different  sperm-cells  and 
germ-cells  ;  it  may  happen  that  two  kindred  individuals  will 
produce  the  ordinary  number  of  offspring,  or  will  produce 
none  ;  or  will  at  one  time  be  fertile  and  at  another  not ;  or 
will  at  one  time  have  offspring  of  tolerable  strength,  and  at 
another  time  feeble  offspring. 

To  the  like  causes  are  also  ascribable  the  phenomena  of 
Variation.  These  are  unobtrusive  while  the  tolerably-uni- 
form conditions  of  a  species  maintain  tolerable  uniformity 
among  the  physiological  units  of  its  members ;  but  they 
become  obtrusive  when   differences  of  conditions,  entailing 


GENESIS,    HEREDITY,    AND   VARIATION.  291 

considerable  functional  differences,  have  entailed  decided  dif- 
ferences among  the  physiological  units ;  and  when  the  differ- 
ent ph}'siologicul  units,  differently  mingled  in  every  individual, 
come  to  be  variously  segregated  and  variously  combined. 

Did  space  permit,  it  might  be  shown  that  this  hypothesis 
is  a  key  to  many  further  facts — to  the  fact  that  mixed  races 
are  comparatively  plastic  under  new  conditions  ;  to  the  fact 
that  pure  races  show  predominant  influences  when  crossed 
with  mixed  races  ;  to  the  fact  that  while  mixed  breeds  are 
often  of  larger  growth,  pure  breeds  are  the  more  hardy — 
have  functions  less-easily  thrown  out  of  balance.  But  with- 
out further  argument,  it  will,  I  think,  be  admitted,  that  the 
power  of  this  hypothesis  to  explain  so  many  phenomena,  and 
to  bring  under  a  common  bond  phenomena  that  seem  so  little 
allied,  is  strong  evidence  of  its  truth.  And  such  evidence 
gains  greatly  in  strength  on  observing  that  this  hypothesis 
brings  the  facts  of  Genesis,  Heredity,  and  Variation  into  har- 
mony with  first  principles.  When  we  see  that  these  plastic 
phvsiological  units,  which  we  find  ourselves  obliged  to  assume, 
are  just  such  more  integrated,  more  heterogeneous,  more  un- 
stable, and  more  multiform  atoms,  as  would  result  from  con- 
tinuance of  the  steps  through  which  organic  matter  is  reached — ■ 
when  we  see  that  the  differentiations  of  them  assumed  to  oc- 
cur in  differently- conditioned  aggregates,  and  the  equilibra- 
tions of  them  assumed  to  occur  in  aggregates  which  maintain 
constant  conditions,  are  but  corollaries  from  those  universal 
principles  implied  by  the  persistence  of  force — when  we  see 
that  the  maintenance  of  life  in  the  successive  generations  of  a 
species,  becomes  a  consequence  of  the  continual  incidence  of 
new  forces  on  the  species,  to  replace  the  forces  that  are  ever 
being  rhythmically  equilibrated  in  the  propagation  of  the 
species — and  when  we  thus  see  that  these  apparently-excep- 
tional phenomena  displayed  in  the  multiplication  of  organic 
beings,  fall  into  their  places  as  results  of  the  general  laws  of 
Evolution ;  we  have  weighty  reasons  for  entertaining  the 
hypothesis  which  affords  us  this  interpretation. 


CHAPTER  XL 

CLASSIFICATION. 

§  98.  That  orderly  arrangement  of  objects  called  Classi- 
fication, has  two  purposes  ;  which,  though  not  absolutely  dis- 
tinct, are  distinct  in  great  part.      It  may  be  employed  to 
facilitate  identification  ;  or  it  may  be  employed  to  organize 
our  knowledge.     If  a  librarian  places  his  books  in  the  alpha- 
betical succession  of  the  author's  names,  he  places  them  in 
such  way  that  any  particular  book  may  easily  be  found ;  but 
not  in  such  way  that  books  of  a  given  nature  stand  together. 
When,  conversely,  he  makes  a  distribution  of  books  accord- 
ing to  their  subjects,  he  neglects  various  superficial  similari- 
ties and  distinctions,  and  groups  them  according  to  certain 
primary  and  secondaiy  and  tertiary  attributes,  which  sever- 
ally imply  many  other  attributes — groups  them  so  that  any 
one  volume  being  inspected,  the  general  characters  of  all  the 
neighbouring  volumes  may  be  inferred.     He  puts  together 
in  one  great  division,  all  works  on  History ;  in  another  all 
Biographical   works  ;    in   another  all   works  that  treat    of 
Science  ;  in  another  Voyages  and  Travels ;  and  so  on.     Each 
of  his  great  groups  he  separates  into  sub-groups ;    as  when 
hf  puts  diiferent  kinds  of  pure  Literature,  under  the  heads 
of   Fiction,  Poetry,    and   the   Drama.      In   some   cases   he 
makes  sub-sub-groups  ;  as  when,  having  divided  his  Scientific 
treatises  into  abstract  and  concrete,  putting  in  the  one  Logic 
and  Mathematics,  and  in  the  other  Physics,  Astronomy,  Ge- 


CLASSIFICATION.  293 

ology,  Chemistry,  Physiology,  &c. ;  he  goes  on  to  sub  divide 
his  books  on  Physics,  into  those  which  treat  of  Mechanical 
Motion,  those  which  treat  of  Heat,  those  which  treat  of  Light, 
of  Electricity,  of  Magnetism. 

Between  these  two  modes  of  classification,  note  the  essen- 
tial distinctions.  Arrangement  according  to  any  single  con- 
spicuous attribute  is  comparatively  easy,  and  is  the  first  that 
suggests  itself :  a  child  may  place  books  in  the  order  of  thc'ii 
sizes,  or  according  to  the  st}'les  of  their  bindings.  But  ar- 
rangement according  to  combinations  of  attributes,  which, 
though  fundamental,  are  not  conspicuous,  requires  analysis  \ 
and  does  not  suggest  itself  till  analysis  has  made  some  pro- 
gress. Even  when  aided  by  the  information  which  the  author 
gives  on  his  title  page,  it  requires  considerable  knowledge  to 
classify  rightly  an  essay  on  Polarization ;  and  in  the  absence 
of  a  title  page,  it  requires  much  more  knowledge.  Again, 
classification  by  a  single  attribute,  which  the  objects  possess 
in  different  degrees,  may  be  more  or  less  serial,  or  linear. 
Books  may  be  put  in  the  order  of  their  dates,  in  single  file ; 
or  if  they  are  grouped  as  works  in  one  volume,  works  in  two 
volumes,  works  in  three  volumes,  &c,  the  groups  may  be 
placed  in  an  ascending  succession.  But  groups  severally 
formed  of  things  distinguished  by  some  common  attribute 
which  implies  man}'  other  attributes,  do  not  admit  of  serial 
arrangement.  You  cannot  rationally  say,  either  that  His- 
torical Works  should  come  before  Scientific  Works,  or  Scien- 
tific Works  before  Historical  Works  ;  nor  of  the  sub-divi- 
?i  >ns  of  creative  Literature,  into  Fiction,  Poetry,  and  the 
Drama,  can  you  give  a  good  reason  why  any  one  should  take 
precedence  of  the  others. 

Hence  this  grouping  of  the  like  and  separation  of  the  un- 
like, which  constitutes  Classification,  can  reach  its  complete 
form  only  by  slow  steps.  We  saw  (First  Principles,  §  36) 
that,  other  things  equal,  the  relations  among  phenomena  are 
recognized  in  the  order  of  their  conspicuousness  ;  and  that, 
nner  things  equal,  they  arc  recognized  in  ihe  order  of  their 


294  THE    INDUCTIONS  CF    BIOLOGY. 

simplicity.  The  first  classifications  are  sure,  therefore,  to  be 
groupings  of  objects  that  resemble  each  other  in  external  or 
easily-perceived  attributes,  and  attributes  that  are  not  of  com- 
plex characters.  Those  likenesses  among  things  which  are 
due  to  their  possession  in  common  of  simple  obvious  properties, 
may  or  may  not  coexist  with  further  likenesses  among  them. 
AYhen  geometrical  figures  are  classed  as  curvilinear  and 
rectilinear,  or  when  the  rectilinear  are  divided  into  trilateral, 
quadrilateral,  &c,  the  distinctions  made,  connote  varioiis 
other  distinctions,  with  which  they  are  necessarily  bound 
up  ;  but  if  liquids  be  classed  according  to  their  visible  cha- 
racters— if  water,  alcohol,  sulphuret  of  carbon,  &c,  be 
grouped  as  colourless  and  transparent,  we  have  things  placed 
together  which  are  unlike  in  their  essential  natures.  Thus, 
where  the  objects  classed  have  numerous  attributes,  the  pro- 
babilities are,  that  the  early  classifications,  based  on  simple 
and  manifest  attributes,  unite  under  the  same  head  many 
objects  that  have  no  resemblances  in  the  majority  of  their 
attributes.  As  the  knowledge  of  objects  increases,  it  be- 
comes possible  to  make  groups  of  which  the  members  have 
more  numerous  properties  in  common ;  and  to  ascertain  what 
property,  or  combination  of  properties,  is  most  characteristic 
of  each  group.  And  the  classification  eventually  arrived  at, 
is  one  in  which  the  segregation  has  been  carried  so  fur,  that 
the  objects  integrated  in  each  group  have  more  attributes  in 
common  with  one  another,  than  they  have  in  common  with 
any  excluded  objects  ;  one  in  which  the  groups  of  such  groups 
are  integrated  on  the  same  principle  ;  and  one  in  which  the 
degrees  of  differentiation  and  integration  are  proportioned  to 
the  degrees  of  intrinsic  unlikeness  and  likeness.  And  the 
ultimate  classification,  while  it  serves  most  completely  to 
identify  the  things,  serves  also  to  express  the  greatest  amount 
of  knowledge  concerning  the  things — enables  us  to  predicate 
the  greatest  number  of  facts  concerning  each  thing ;  and  by 
so  doing  proves  that  it  expresses  the  most  precise  corre- 
spondence between  our  conceptions  and  the  realities. 


CLASSIFICATION.  295 

§  99.  Biological  classifications  illustrate  well  these  phases, 
ill  rough  which  classifications  in  general  necessarily  pass 
In  early  attempts  to  arrange  organic  beings  in  some  sjs- 
tematic  manner,  we  see  at  first,  a  guidance  by  conspicuous 
and  simple  characters,  and  a  tendency  towards  arrangement 
in  linear  order.  In  successively  later  attempts,  we  see 
more  regard  paid  to  combinations  of  characters  which  are 
essential  but  often  inconspicuous ;  and  a  gradual  abandon- 
ment of  a  linear  arrangement  for  an  arrangement  in  di- 
vergent groups  and  re-divergent  sub-groups. 

In  the  popular  mind,  plants  are  still  classed  under  the 
heads  of  Trees,  Shrubs,  and  Herbs  ;  and  this  serial  classing 
according  to  the  single  attribute  of  magnitude,  swayed  the 
earliest  observers.  They  would  have  thought  it  absurd  to 
call  a  bamboo,  thirty  feet  high,  a  kind  of  grass  ;  and  would 
have  been  incredulous  if  told  that  the  Hart's-tongue  should 
be  placed  in  the  same  great  division  with  the  Tree-ferns 
The  zoological  classifications  that  were  current  before  Na- 
tural History  became  a  science,  had  divisions  similarly  super- 
ficial and  simple.  Beasts,  Birds,  Fishes,  and  Creeping-things, 
are  names  of  groups  marked  off  from  one  another  by  con- 
spicuous differences  of  appearance  and  modes  of  life — crea- 
tures that  walk  and  run,  creatures  that  fly,  creatures  that  live 
in  the  water,  creatures  that  crawl.  And  these  groups  were 
thought  of  in  the  order  of  their  importance. 

The  first  arrangements  made  by  naturalists  were  based 
either  on  single  characters,  or  on  very  simple  combinations 
of  characters.  Describing  plant-classifications,  Lindley 
Bays  :  —  "  Rivinus  invented,  in  1690,  a  system  depend- 
ing upon  the  formation  of  the  corolla  ;  Kamel,  in  1693, 
upon  the  fruit  alone ;  Magnol,  in  1720,  on  the  calyx  and 
corolla  ;  and  finally,  Linnaeus,  in  1731,  on  variations  in  the 
stamens  and  pistil."  In  this  last  system,  which  has  been  for 
so  long  current  as  a  means  of  identification,  simple  external 
attributes  are  still  depended  on ;  and  an  arrangement,  in 
great  measure  serial,  is  based  on  the  degrees  in  which  thebc 


296  rilE    INDUCTIONS    OF    BIOLOGY. 

attributes  are  possessed.  In  1703,  some  tLirty  years  before 
the  time  of  Linnoeus,  our  countryman  Ray  had  sketched  the 
outlines  of  a  more  advanced  system.     He  said  that — 

Plants  are  either 

Flowerless,  or 

Flowering ;  and  these  are 
Dicotyledones,  or 
Monocotyledones. 
Among   the   minor   groups   which   he    placed   under   these 
general   heads,   "  were   Fungi,    Mosses,    Ferns,   Composites, 
CichoraceaB  Umbellifers,  Papilionaceous  plants,  Conifers,  La- 
biates, &c,  under  other  names,  but  with  limits  not  very  dif- 
ferent from  those  now  assigned  to  them."     Being  much  in 
advance  of  his  age,  Ray's  ideas  remained  dormant  until  the 
time  of  Jussieu ;  by  whom  they  were  developed  into  what 
has  become  known  as  the  Natural  System.     Passing  through 
various  modifications  in  the  hands  of  successive  botanists, 
the  Natural  System  has  now  taken  the  following  form ;  which 
I    copy    (adding   the  alliances   to   the   classes)    from   Prof. 
Lindley 's  Vegetable  Kingdom.* 

*  From  this  table  I  have  omitted  the  class  RMzogcm,  which  other  botanists 
do  not  agree  with  Lindley  in  regarding  as  a  separate  class.  The  plants  respect- 
ing  which  there  has  arisen  this  difference  of  opinion,  are  certain  flowering 
plants,  which  grow  parasitically  on  the  roots  of  trees.  The  reasons  assigned  bv 
Endlicher  and  Lindley,  for  erecting  them  into  a  separate  group  of  Phaenogams, 
are,  that  in  place  of  true  leaves  they  have  only  cellular  scales ;  that  the  stem  is 
an  amorphous  fungous  mass,  imperfectly  supplied  with  spiral  vessels ;  ana  :n:it 
they  are  without  chlorophyll.  Mr  Griffith  and  Dr  Hooker,  however,  have  gr  <  u 
preponderating  reasons  why  they  should  be  restored  to  the  class  Exogens.  It 
seems  here  worth  remarking,  that  certain  zoological  facts  suggest  an  explanation 
of  these  anomalous  botanical  facts;  and  confirm  the  conclusion  reached  by  Dr 
Hooker  and  Mr  Griffith.  It  very  commonly  happens  that  animal-parasites  arc 
aberrant  forms  of  the  types  to  which  they  belong ;  and,  by  analogy,  we  may  not 
unieasonably  expect  to  find  among  parasitic  plants,  the  most  aberrant  forms  of 
vegetal  types.  More  than  this  is  true.  The  kind  of  aberration  which  we  see  in  the 
one  case,  we  see  in  the  other ;  and  in  both  cases,  the  meaning  of  the  aberration  is 
manifest.  In  such  Epizoa  as  the  Lernece,  the  Crustacean  type  is  disguised  by  the 
almost  entire  loss  of  the  limbs  and  organs  of  sense,  by  the  simplification  of  the 
digestive  apparatus,  and  by  the  great  development  of  the  reproductive  system; 


CLASSIFICATION. 


297 


Asexual,  or  Flower  less  Plants. 

{Algales 
Fungales 
Lichenalee 
_  ,  ,  ,.    .        .  ,    . ,  rMuscalea 

Stems  and  leaves  distinguishable         II.  Acbogens     <  Lycopodalea 

^Filicales 

Sexual,  or  Flowering  Plants. 

(Glumales 
Arales 
Palmalos 

J  Hydra]  ea 
Narcissalea 
Amomales 
Orchidales 
Xyridales 
Juncales 
Liliales 
LAlisinales 

IV.    DlCTTOGENS. 


Wood  of  stem  youngest  in  centre ; 
cotyledon  single. 

Leaves  parallel-veined,  permanent ; 
wood  confused 


Leaves  net -veined,  deciduous ; 
wood,  when  perennial,  arranged 
in  a  circle  with  a  central  pith 

Wood  of  stem  youngest  at  circum- 
ference, always  concentric ;  coty- 
ledons two  or  more. 

Seeds  quite  naked 


V.  Gtmnogens. 

'Diclinous 


Keeds  enclosed  in  seed-vessels 


VL  Exogens 


Hypogynous 


Perigynous 


Epigynous 


{Amen  tales 
Urtieales 
Euphorbialos 
&c.  Ac. 
rViolales 
J  Cistales 
I  Malvaies 
*•    &e.  Ac. 
fFicoidales 
J  Daphnales 
|  Rosales 
*■    &c.  Ac. 

{Campanalea 
Mvrtales 
Cactales 
Ac.  Ac. 

Here,  linear  arrangement  has  disappeared :  there  is  a 
breaking  up  into  groups  and  sub-groups  and  sub-sub-groups, 
which  do  not  admit  of  being  placed  in  serial  order,  but  only 
in  divergent  and  re-divergent  order.  Were  there  space  to 
exhibit  the  way  in  which  the  Alliances  are  subdivided  into 
Orders,  and  these  into  Genera,  and  these  into  Species  ;  the 

the  parts  no  longer  needed,  abort,  and  those  parts  develop  which  favour  the 
preservation  of  the  race.  Similarly  in  the  Rhizogens,  the  abortive  development 
of  the  leaves,  the  absence  of  chloropnyll,  and  the  imperfect  supply  of  spiral 
vessels,  are  changes  towards  a  structure  fit  for  a  plant  which  lives  on  the  juices 
absorbed  from  another  plant;  while  the  rapid  and  great  development  of  the 
fructifying  organs,  are  correlative  changes  advantageous  to  a  plant,  the  seeds  of 
which  have  but  small  chances  of  rooting  themselves.  And  just  the  same  reason 
that  exists  for  the  production  of  immensely  numerous  but  extremely  small  eggs 
by  Entozoa,  exists  for  the  production  by  Rhizogens^  of  seeds  that  are  grcul  in 
uuniber  and  almost  spore-like  in  size. 
20 


298  THE    INDUCTIONS   OF    BIOLOGY. 

same  principle  of  co-ordination  would,  be  still  further  mani- 
fested. On  studying  the  definitions  of  these  primary,  se- 
condary, and  tertiary  classes,  it  will  be  found,  that  the 
largest  are  marked  off  from  each  other  by  some  attribute 
which  connotes  sundry  other  attributes  ;  that  each  of  the 
smaller  classes  comprehended  in  one  of  these  largest  classes, 
is  marked  off  in  a  similar  way  from  the  smaller  classes 
bound  up  with  it ;  and  that  so,  each  successively  smaller 
class,  has  an  increased  number  of  co-existing  attributes. 

§  100.  Zoological  classification  has  had.  a  parallel  history. 
The  first  attempt  which  we  need  notice,  to  arrange  animals 
in  such  a  way  as  to  display  their  affinities,  is  that  of  Lin- 
naeus.    He  grouped  them  thus  :* — 

Cl.  1.  Mammalia.  Ord.  Primates,  Bruta,  Ferae,  Glires,  Pecora,  Belluse, 
Cete. 

Cl.  2.  Aves.  Ord.  Accipitres,  Picse,  Anseres,  Grallae,  Galliuae,  Passeres. 

Cl.  3.  Amphibia.  Ord.  Reptiles,  Serpentes,  Nantes. 

Cl.  4.  Pisces.  Ord.  Apodes,  Jugulares,  Thoracici,  Abdominales. 

Cl.  5.  Insecta.  Ord.  Coleoptera,  Hemiptera,  Lepidoptera,  Neuroptera, 
Diptera,  Aptera. 

Cl.  6.  Vermes.  Ord.  Intestiua,  Mollusca,  Testacea,  Lithophyta,  Zoo- 
phyta. 

This  arrangement  of  classes,  is  obviously  based  on  ap- 
parent gradations  of  rank ;  and  the  placing  of  the  orders 
similarly  betrays  an  endeavour  to  make  successions,  begin- 
ning with  the  most  superior  forms  and  ending  with  the 
most  inferior  forms.  While  the  general  and  vague  idea 
of  perfection,  determines  the  leading  character  of  the 
classification,  its  detailed  groupings  are  determined  by 
the  most  conspicuous  external  attributes.  Not  only  Lin- 
naeus, but  his  opponents,  who  proposed  other  systems,  were 
"  under  the  impression  that  animals  were  to  be  arranged 
together  into  classes,  orders,  genera,  and  species,  according  to 
their  more  or  less  close  external  resemblance."  This  con- 
ception survived  till   the   time   of  Cuvier.     "Naturalists." 

*  This  classification,  and  the  three  which  iuiiow  it,  1  quote  (aunagmg  mjuip 
of  thiuii)  from  Prof.  Agassiz's  "Essay  on  Classification." 


CLASSIFICATION.  299 

says  Agassiz,  "were  bent  upon  establishing  one  continual 
uniform  series  to  embrace  all  animals,  between  the  links  of 
which  it  was  supposed  there  were  no  unequal  intervals. 
The  watchword  of  their  school  was :  Natura  non  facit 
talfum.     They  called  tl.eir  system  la  chaine  dcs  etres." 

The  classification  of  Cuvier,  based  on  internal  organization 
instead  of  external  appearance,  was  a  great  advance.  Ho 
asserted  that  there  are  four  principal  forms,  or  four  general 
plans,  on  which  animals  are  constructed ;  and  in  pursuance 
of  this  assertion,  he  drew  out  the  following  scheme. 

First  Branch.     Animalia  Vertebrata 
Cl.  1.  Mammalia. 
Cl.  2.  Birds. 
Cl.  3.  Reptilia. 
Cl.  4.  Fishes. 

Second  Branch.     Animalia  Mollusca. 
Cl.  1.  Cephalapoda. 
Cl.  2.  Pteropoda. 
Cl.  3.  Gasteropoda. 
Cl.  4.  Acephala. 
Cl.  5.  Brachiopoda. 
Cl.  6.  Cirrhopoda. 

Third  Branch.     Animalia  Articulate  . 
Cl.  1.  Annelides. 
Cl.  2.  Crustacea. 
Cl.  3.  Arachnides. 
Cl.  4.  Insects. 

Fourth  Branch.     Animalia  Radiata. 

Cl.    1.    ECHINODERMS. 

Cl.  2.  Intestinal  "Worms. 

Cl.  3.  AcAi,EPiLra. 

Ol.  4.  Polypi. 

Cl.  o.  Infusoria, 


300 


THE    INDUCTIONS    OF  BIOLOGY. 


But  though  Cuvier  emancipated  himself  from  the  concep- 
tion of  a  serial  progression  throughout  the  Animal- King- 
dom ;  sundry  of  his  contemporaries  and  successors  remained 
fettered  by  the  old  error.  Less  regardful  of  the  differently- 
co-ordinated  sets  of  attributes  displayed  by  the  different  sub- 
kingdoms  ;  and  swayed  by  the  belief  in  a  progressive  develop- 
ment, which  was  erroneously  supposed  to  imply  the  possibility 
of  arranging  animals  in  a  linear  series  ;  they  persisted  in 
thrusting  organic  forms  into  a  quite  unnatural  order.  The 
following  classification  of  Lamarck  illustrates  this. 

INVERTEBRATA. 


I.     Apathetic  Animals. 


II. 


Cl. 

1. 

Infusoria. 

Cl. 

2. 

Polypi. 

Cl. 

3. 

Radiaria. 

Cl. 

4. 

TUNICATA. 

Cl. 

5. 

Yermes. 

Sensitive  Animals. 

Cl. 

6. 

Insects. 

Cl. 

7. 

Arachnids. 

Cl. 

8. 

Crustacea. 

Cl. 

9. 

Annelids. 

Cl. 

10. 

Cirripeds. 

Cl. 

11. 

Conchifera. 

Cl. 

12. 

MOLLUSKS. 

III.     Intelligent  Animals 


Cl. 

13. 

Fishes. 

Cl 

14. 

Reptiles. 

Cl. 

15. 

Birds. 

Cl. 

16. 

Mammaija 

Do  not  feel,  and  move  only  by 
their  excited  irritability.  No  brain, 
not  elongated  medullary  mass;  no 
senses ;  forms  varied ;  rarely  articu- 
lations. 


Feel,  but  obtain  from  their  sensa- 
tions only  perceptions  of  objects,  a 
sort  of  simple  ideas,  which  they  are 
unable  to  combine  to  obtain  complex 
)■  ones.  No  vertebral  column ;  a  brain 
and  mostly  an  elongated  medullary 
mass;  some  distinct  senses;  muscles 
attached  under  the  skin ;  form  sym- 
metrical, the  parts  being  in  pairs. 


VERTEBRATA. 

Feel;  acquire  preservable  ideas; 
perform  with  them  operations  by 
which  they  obtain  others ;  are  intel- 
ligent in  different  degrees.  A  ver- 
•  tebral  column ;  a  brain  and  a  spinal 
marrow ;  distinct  senses ;  the  mus- 
cles attached  to  the  internal  skele- 
ton ;  form  symmetrical,  the  parts 
being  in  pairs. 


CLASSIFICATION,  301 

Passing  over  sundry  classifications  in  which  the  serial 
arrangement  dictated  b}r  the  notion  of  ascending  complexity, 
is  variously  modified  by  the  recognition  of  conspicuous 
anatomical  facts,  we  come  to  the  classifications  which  recognize 
another  order  of  facts — those  of  development.  The  embryo- 
logical  inquiries  of  Von  Baer,  led  him  to  arrange  animals  as 
follows  : — 

I.  Peripheric  Type.  (Rapiata.)  Evolutio  radiata.  The 
development  proceeds  from  a  centre,  producing 
identical  parts  in  a  radiating  order. 
II.  Massive  Type.  (Mollusca.)  Evolutio  contorta.  The 
development  produces  identical  parts  curved  around 
a  conical  or  other  space. 

III.  Longitudinal  Type.    (Artictjlata.)    Evolutio  gemina. 

The  development  produces  identical  parts  arising  on 
both  sides  of  an  axis,  and  closing  up  along  a  line 
opposite  the  axis. 

IV.  Doubly  Symmetrical  type.     (Vertebrata.)    Evolutio 

bigemina.  The  development  produces  identical 
parts  arising  on  both  sides  of  an  axis,  growing  up- 
wards and  downwards,  and  shutting  up  along  two 
lines,  so  that  the  inner  layer  of  the  germ  is  inclosed 
below,  and  the  upper  layer  above.  The  embryos  of 
these  animals  have  a  dorsal  cord,  dorsal  plates,  and 
ventral  plates,  a  nervous  tube  and  branchial  fissures. 

Recognizing  these  fundamental  differences  in  the  modes  of 
evolution,  as  answering  to  fundamental  divisions  in  the 
animal  kingdom,  Von  Baer  shows  (among  the  Vertebrata  at 
least)  how  the  minor  differences  that  arise  at  successively 
later  stages  of  evolution,  correspond  with  the  minor  divisions. 

Like  the  modern  classification  of  plants,  the  classification 
of  animals  that  has  now  been  arrived  at,  is  one  in  which  the 
linear  older  is  completely  broken  up.  In  his  lectures  at  the 
Royal  Iustitution,  in  1857,  Prof.  Huxley  expressed  the  rela- 


302  THE    INDUCTIONS   OF    BIOLOGY. 

tions  existing  among  the  several  great  groups  of  the  animal 
kingdom,  by  placing  these  groups  at  the  ends  of  four  or  five 
radii,  diverging  from  a  centre.  The  diagram  I  cannot 
obtain ;  but  in  the  published  reports  of  his  lectures  at  the 
School  of  Mines  the  groups  were  arranged  thus : — 


Vertebrata 

{Abranchiala) 

Mammalia 

Aves 

Beptilia 

[Branehiata) 

Amphibia 

Pisces 

MOLLUSCA 

Annulosa 

Cephalopoda   Heteropoda 

) 

Articulata 

Gasteropoda- 

•    >                 Insecta 

Arachnids 

dioecia 

)                  Myriapoda          Crustacea 

(  Pulmonata      Gasteropoda- 

\  Pteropoda            moncecia 

Annuloida 

Laniellibranchiata 

Annellata                Scoleidse 

Echinodermata        Trematoda 

Rotifera 

Toeniadae 
Turbellaria 

• 

Nematoidea 

C(ELENTERATA 

Hydrozoa 

Actinozoa. 

Protozoa 

Infusoria 

Spongiadae 

Gregarinidae 

Noctilucida 

Foraminifera 

ThaUassicollidce 

What  remnant  there  may  seem  to  be  of  linear  succession 
in  some  of  these  sub-groups,  is  merely  an  accident  of  typo- 
graphical convenience.  Each  of  them  is  to  be  regarded 
simpby  as  a  cluster.  Were  Prof.  Huxley  now  to  revise  this 
scheme,  he  would  probably  separate  more  completely  some  of 
the  great  sub-groups,  in  conformity  with  the  views  expressed 
in  his  Hunterian  Lectures  delivered  at  the  College  of  Sur- 
geons in  1863.  And  if  he  were  further  to  develop  the 
arrangement,  by  dispersing  the  sub-groups  and  sub-sub- 
groups on  the  same  principle,  there  would  result  an  arrange- 


CLASSIFICATION.  303 

ment  perhaps  not  very  much  unlike  that  shown  in  the  an- 
nexed diagram. 


•      • 


•   WM'amma/c'n  .  », 

•        .  •  ''.Atm 

'  .'.  I    Br/itilln. 

V  E   RTEB'RATA 


A-mfikibia     \  Pisces 

\       • 


•  •  • 
\  .*  .'*  Crustacea 

\ 

I  .Alj/ria/ica'a 

I 

ANNl/LOSA 

^  jAnnclida^ 

\  frcleci!da     ' 

\  ij  •  • 

\  A/Tiuuloida. 

Ptcrcficda  .'OfiAaAJMt  \  Ec\dncdcrfaata\\' 


\ 


\ 
\ 


.  ,GastfTof>cda 
'   •    dicecia  \  I 


Gastercficda.  •  ^Putmonata 

mcnacia    %  • 


/        / 


MOLLUSCA  \  / 

Lamelli6ra.nc/iiafa~~—-~.  \  /     / 

""■^-^  '   ' 

\BracAU/icd&  •  m»Gregari-nid* 

Mollus  c  oTda--  ji/Ute/tcdq -\^ 

AscidMda  *  •  *  .* "  'Pclya  o  a.  /PROTOZOA 

•  /                  .  -      . 

•  .  /  Shcnqida  Infuscvttt 

xr  j          •/•  m              *    •  ••• 

JHydrfiBca  /.     •.  • 

j 

CCELEN  TERATA 

jLctincsca' 


In  this  diagram,  the  dots  represent  orders,  the  names  ot 
which  it  is  impracticable  to  insert.  If  it  be  supposed  that 
when  magnified,  each  of  these  dots  resolves  itself  into  a 
cluster  of  clusters,  representing  genera  and  species,  an  ap- 
proximate idea  will  be  formed  of  the  relations  among  the 
successively-subordinate  groups  constituting  the  animal  king- 


304  THE    INDUCTIONS    OF    BIOLOGY. 

dom.  Besides  the  subordination  of  groups  and  their  general 
distribution,  some  other  facts  are  indicated.  By  the  distances 
of  the  great  divisions  from  the  general  centre,  are  rudely 
symbolized  their  respective  degrees  of  divergence  from  the 
form  of  simple,  undifferentiated  organic  matter;  which  we 
mav  regard  as  their  common  source.  Within  each  group, 
the  remoteness  from  the  local  centre  represents,  in  a  rough 
way,  the  degree  of  departure  from  the  general  plan  of  the 
group.  And  the  distribution  of  the  sub-groups  within  each 
group,  is  in  most  cases  such,  that  those  which  come  nearest 
to  neighbouring  groups,  are  those  which  show  the  nearest 
resemblances  to  them — in  their  analogies  though  not  in  their 
homologies.  No  diagram,  however,  can  give  a  correct  con- 
ception. Even  supposing  the  above  diagram  expressed  the 
relations  of  animals  to  one  another  as  truly  as  they  can  be 
expressed  on  a  plane  surface,  (which  of  course  it  does  not,)  it 
would  still  be  inadequate.  Such  relations  cannot  be  repre- 
sented in  space  of  two  dimensions ;  but  only  in  space  of  three 
dimensions 

§  101.  While  the  classifications  of  botanists  and  zoologists 
have  become  more  and  more  natural  in  their  arrangements, 
there  has  grown  up  a  certain  artificiality  in  their  abstract 
nomenclature.  When  aggregating  the  smallest  groups  into 
larger  groups,  and  these  into  groups  still  larger,  natur- 
alists adopted  certain  general  terms  expressive  of  the  suc- 
cessively more  comprehensive  divisions ;  and  the  habitual 
use  of  these  terms,  needful  for  purposes  of  convenience,  has 
led  to  the  tacit  assumption  that  they  answer  to  actualities  in 
Nature.  It  has  been  taken  for  granted  that  species,  genera, 
orders,  and  classes,  are  assemblages  of  definite  values — that 
every  genus  is  the  equivalent  of  every  other  genus,  in  respect 
of  its  degree  of  distinctness ;  and  that  orders  are  separated 
by  lines  of  demarcation  that  are  as  broad  in  one  place  as 
another.  Though  this  conviction  is  not  a  formulated  one, 
yet  the  disputes  continually  arising  among  naturalists  on  tho 


CLASSIFICATION.  305 

questions,  whether  such  and  such  organisms  are  specifically 
or  generically  distinct,  and  whether  this  or  that  peculiarity 
is  or  is  not  of  ordinal  importance,  imply  that  the  conviction 
is  entertained  even  where  it  is  not  avowed.  Yet  that  dif- 
ferences of  opinion  like  these  continually  arise,  and  remain 
unsettled,  except  when  they  end  in  the  establishment  of  sub- 
species, sub-genera,  sub-orders,  and  sub-classes,  sufficiently 
shows  that  no  such  conviction  is  justifiable.  And  this  ia 
equally  shown  by  the  impossibility  of  obtaining  an}r  definition 
of  the  degree  of  difference,  which  warrants  each  further  eleva- 
tion in  the  hierarchy  of  classes. 

It  is,  indeed,  a  wholly  gratuitous  assumption  that  organ- 
isms admit  of  being  placed  in  groups  of  equivalent  values  ; 
and  that  these  may  be  united  into  larger  groups  that  are 
also  of  equivalent  values  ;  and  so  on.  There  is  no  a  priori 
reason  for  expecting  this  ;  and  there  is  no  a  posteriori  evi- 
dence implying  it,  save  that  which  begs  the  question — that 
which  asserts  one  distinction  to  be  generic  and  another  to  be 
ordinal,  because  it  is  assumed  that  such  distinctions  must  be 
either  generic  or  ordinal.  The  endeavour  to  thrust  plants 
and  animals  into  these  definite  partitions,  is  of  the  same 
nature  as  the  endeavour  to  thrust  them  into  a  linear  series. 
Not  that  it  does  violence  to  the  facts  in  anything  like  the 
same  degree ;  but  still,  it  does  violence  to  the  facts.  Doubt- 
less the  making  of  divisions  and  sub-divisions,  is  extremely 
useful ;  or  rather,  it  is  absolutely  necessary.  Doubtless,  too, 
in  reducing  the  facts  to  something  like  order,  they  must  be 
partially  distorted.  So  long  a3  the  distorted  form  is  not 
mistaken  for  the  actual  form;  no  harm  results.  But  it  is 
needful  for  us  to  remember,  that  while  our  successively 
subordinate  groups  have  a  certain  general  correspondence 
with  the  realities,  they  inevitably  give  to  the  realities  a 
regularity  which  does  not  exist. 

§  102.  A  general  truth  of  much  significance  is  exhibited 
in  these  classifications.     On  observing  the  natures   of  the 


306  THE    INDUCTIONS   OF    BIOLOGY. 

attributes  which  are  common  to  the  members  of  any  group 
of  the  first,  second,  third,  or  fourth  rank,  we  see  that  groups 
of  the  widest  generality  are  based  on  characteristics  of  the 
greatest  importance,  physiologically  considered  ;  and  that  the 
characteristics  of  the  successively- subordinate  groups,  are 
characteristics  of  successively -subordinate  importance.  The 
structural  peculiarity  in  which  all  members  of  one  sub- 
kingdom  differ  from  all  members  of  another  sub-kingdom,  is 
a  peculiarity  that  affects  the  vital  actions  more  profoundly, 
than  does  the  structural  peculiarity  which  distinguishes  all 
members  of  one  class  from  all  members  of  another  class. 
Let  us  look  at  a  few  cases. 

We  saw  (§  56),  that  the  broadest  division  among  the 
functions  is  the  division  into  "  the  accumulation  of  force 
(latent  in  food)  ;  the  expenditure  of  force  (latent  in  the 
tissues  and  certain  matters  absorbed  by  them) ;  and  the 
transfer  of  force  (latent  in  the  prepared  nutriment  or  blood) 
from  the  parts  which  accumulate  to  the  parts  which  expend." 
Now  the  lowest  animals,  united  under  the  general  name 
Protozoa,  are  those  in  which  there  is  either  no  separation  of 
the  parts  performing  these  functions  or  very  indistinct  separ- 
ation :  in  the  Rhizopoda,  all  parts  are  alike  accumulators  of 
force,  expenders  of  force,  and  transferrers  of  force;  and 
though  in  the  most  differentiated  members  of  the  group,  the 
Infusoria,  there  are  something  like  specializations  corre- 
sponding to  these  functions,  yet  there  are  no  distinct  tissues 
appropriated  to  them.  The  animals  known  as  Cceknterata 
are  characterized  in  common  by  the  possession  of  a  part 
which  accumulates  force  more  or  less  marked  off  from  the 
part  which  does  not  accumulate  force,  but  only  expends  it ; 
and  the  Hydrozoa  and  Actinozoa,  which  are  sub-divisions  of 
the  Ccelenterata,  are  contrasted  in  this,  that  in  the  one  these 
parts  are  very  indefinitely  distinguished,  but  in  the  other 
definitely  separated,  as  well  as  more  complicated.  Besides  a 
completer  differentiation  of  the  organs  respectively  devoted 
to  the  accumulation  of  force  and  the  expenditiire  of  force, 


CLASSIFICATION.  307 

the  animals  classed  as  Molluscoida,  possess  rude  appliances 
for  the  transfer  of  force :  the  peri- visceral  sac,  or  closed 
cavity  between  the  intestine  and  the  walls  of  the  body, 
serves  as  a  reservoir  of  absorbed  nutriment,  from  which  the 
surrounding  tissues  take  up  the  materials  they  need.  The 
more  highly-organized  animals,  belonging  to  whichever  sub- 
kingdom,  all  of  them  possess  definitely-constructed  channels 
for  the  transfer  of  force ;  and  in  all  of  them,  the  function  of 
expenditure  is  divided  between  a  directive  apparatus  and 
an  executive  apparatus — a  nervous  system  and  a  muscular 
system.  But  these  higher  sub-kingdoms  are  clearly  separated 
from  each  other  by  differences  in  the  relative  positions  of 
their  component  sets  of  organs.  Prof.  Huxley  defines  the 
type  of  the  Vertebrata,  as  one  in  which  the  ganglionic  nervous 
system  lies  on  the  dorsal  side  of  the  alimentary  canal,  while 
the  central  vascular  system  lies  on  its  ventral  side ;  and  one 
which  is  yet  further  characterized  by  the  possession  of  a 
second,  and  more  conspicuous,  nervous  system,  placed  on  the 
dorsal  side  of  the  vertebral  axis — an  extra  endowment  which 
is  perhaps  the  most  essentially  distinctive.  The  types  of  the 
Annulosa  and  Mollusca,  are  together  marked  off  from  the 
vertebrate  type,  by  the  singleness  of  the  nervous  system,  and 
by  its  occupation  of  the  ventral  side  of  the  body :  the 
habitual  attitudes  of  annulose  and  molluscous  creatures,  is 
such  that  the  neural  centres  are  below  the  alimentary  canal 
and  the  haemal  centres  above.  And  while  by  these  traits  the 
annulose  and  molluscous  types  are  separated  from  the  verte- 
brate, they  are  separated  from  each  other  by  this,  that  in 
the  one  the  body  is  "  composed  of  successive  segments, ' 
usually  provided  with  limbs,"  but  the  other,  the  body  is  not 
segmented,  "  and  no  true  articulated  limbs  are  ever  de- 
veloped." 

The  sub-kingdoms  being  thus  distinguished  from  one  an- 
other, by  the  presence  or  absence  of  parts  devoted  to  funda- 
mental functions,  or  else  by  differences  in  the  distributions  of 
such  parts  ;  we  find,  on  descending  to  the  classes,  that  these 


308  THE   INDUCTIONS   OF    BIOLOGY. 

are  distinguished  from  each  other,  either  by  modifications  in 
the  structures  of  fundamental  parts,  or  by  the  presence  or 
absence  of  subsidiary  parts,  or  by  both.  Fishes  and.  Am- 
phibia are  unlike  higher  vertebrates-  in  possessing  branchiae; 
either  throughout  life  or  early  in  life.  And  every  higher 
vertebrate,  besides  having  lungs,  is  characterized  by  having, 
during  development,  an  amnion  and  an  allantois.  Mammals, 
again,  are  marked  off  from  Birds  and  Reptiles  by  the 
presence  of  mammae,  as  well  as  by  the  form  of  the  occipital 
condyles.  Among  Mammals,  the  next  division  is  based  on 
the  presence  or  absence  of  a  placenta.  And  divisions  of  the 
Placentalia  are  mainly  determined  by  the  characters  of  the 
organs  of  external  action. 

Thus,  without  multiplying  illustrations  and  without  de- 
scending to  genera  and  species,  we  see  that,  speaking  gener- 
ally, the  successively  smaller  groups,  are  distinguished  from 
one  another  by  traits  of  successively  less  importance,  physio- 
logically considered.  The  attributes  possessed  in  common 
by  the  largest  assemblages  of  organisms,  are  few  in  number 
but  all-essential  in  kind — affect  fundamentally  the  most  vital 
actions.  Each  secondary  assemblage,  included  in  one  of  the 
primary  assemblages,  is  characterized  by  further  common 
attributes  that  influence  the  functions  less  profoundly.  And 
bo  on  with  each  lower  grade  of  assemblage. 

5  103.  "WTiat  interpretation  is  to  be  put  on  these  truths  of 
classification  ?  We  find  that  organic  forms  admit  of  an 
arrangement  everywhere  expressive  of  the  fact,  that  along 
with  certain  attributes,  certain  other  attributes,  which  are 
not  directly  connected  with  them,  always  exist.  How  are 
we  to  account  for  this  fact  ?  And  how  are  we  to  account  for 
the  fact  that  the  attributes  possessed  in  common  by  the 
largest  assemblages  of  forms,  are  the  most  vitally-important 
attributes  ? 

No  one  can  believe  that  combinations  of  this  kind  may 
have  arisen  fortuitously.     Or  if  any  one  believes  this,  it  ie 


CLASSIFICATION.  309 

easy  to  prove  to  him  that  the  law  of  probabilities  negatives 
the  assumption.  Even  supposing  fortuitous  combinations  of 
attributes  might  result  in  organisms  that  would  work,  we 
should  still  be  without  a  clue  to  this  special  mode  of  com- 
bination. The  chances  would  be  infinity  to  one  against 
organisms  which  possessed  in  common  certain  fundamental 
attributes,  having  also  in  common  numerous  non-essential 
attributes. 

No  one,  again,  can  allege  that  such  combinations  are 
necessary,  in  the  sense  that  all  other  combinations  are  im- 
practicable. There  is  not,  in  the  nature  of  things,  any 
reason  why  creatures  covered  with  feathers  should  always 
have  beaks  :  jaws  holding  teeth  would,  in  many  cases, 
have  served  them  equally  well  or  better.  The  most  general 
characteristic  of  an  entire  sub-kingdom,  equal  in  extent 
to  the  Vertebrata,  might  have  been  the  possession  of  nicti- 
tating membranes ;  while  the  internal  organizations  through- 
out this  sub-kingdom,  might  have  been  on  many  different 
plans. 

If,  on  the  other  hand,  this  peculiar  subordination  of  attri- 
butes which  organic  forms  display,  be  ascribed  to  design,  other 
difficulties  suggest  themselves.  To  suppose  that  a  certain 
plan  of  organization  was  fixed  on  by  a  Creator,  for  each  vast 
and  varied  group,  the  members  of  which  were  to  lead  many 
different  modes  of  life  ;  and  that  he  bound  himself  to  adhere 
rigidly  to  this  plan,  even  in  the  most  aberrant  forms  of  the 
group,  where  some  other  plan  would  have  been  more  appro- 
priate ;  is  to  ascribe  a  very  strange  motive.  When  we  dis- 
cover that  the  possession  of  seven  cervical  vertebrae  is  a 
general  characteristic  of  mammals,  whether  the  neck  be  im- 
mensely long,  as  in  the  giraffe,  or  quite  rudimentary,  as  in 
the  whale  ;  shall  we  say  that  though,  for  the  whale's  neck, 
one  vertebra  would  have  been  equally  good,  and  though,  for 
the  giraffe's  neck,  a  dozen  would  probably  have  been  better 
than  seven,  yet  seven  was  the  number  adhered  to  in  both 
cases,  because  seven  was  fixed  upon  for  the  mammalian  type  ? 


310  THE    INDUCTIONS   OF    BIOLOGY. 

And  then,  when  it  turns  out  that  this  possession  of  seven 
cervical  vertebrae  is  not  an  absolutely-universal  characteristic 
of  mammals,  shall  we  conclude  that  while,  in  a  host  of  cases, 
there  is  a  needless  adherence  to  a  plan  for  the  sake  of 
consistency,  there  is  yet,  in  some  cases,  an  inconsistent 
abandonment  of  the  plan  ?  I  think  we  may  properly  refuse 
to  draw  any  such  conclusion. 

What,  then,  is  the  meaning  of  these  peculiar  relations  of 
organic  forms  ?  The  answer  to  this  question  must  be  post- 
poned. Having  here  contemplated  the  problem  as  presented 
in  these  wide  inductions  which  naturalists  have  reached ;  and 
having  seen  what  proposed  solutions  of  it  are  inadmissible ; 
we  shall  see,  in  the  next  division  of  this  work,  what  is  the 
only  possible  solution. 


CHAPTER   XII. 

DISTRIBUTION. 

§  104.  There  is  a  distribution  of  organisms  in  Space,  and 
there  is  a  distribution  of  organisms  in  Time.  Looking  first 
at  their  distribution  in  Space,  we  observe  in  it  two  different 
classes  of  facts.  On  the  one  hand,  the  plants  and  animals  of 
each  species,  manifestly  have  their  habitats  limited  by  ex 
ternal  conditions :  they  are  necessarily  restricted  to  spacea 
in  which  their  vital  actions  can  be  performed.  On  the  other 
hand,  the  existence  of  certain  conditions  does  not  determine 
the  presence  of  organisms  that  are  the  fittest  for  them  :  there 
are  many  spaces  perfectly  adapted  for  life  of  a  high  order, 
in  which  only  life  of  a  much  lower  order  is  found.  While, 
in  this  inevitable  restriction  of  organisms  to  environments 
with  which  their  natures  correspond,  we  find  a  negative 
cause  of  distribution  ;  there  remains  to  be  found  that  positive 
cause  of  distribution,  whence  results  the  presence  of  organ- 
isms in  some  of  the  places  appropriate  to  them,  and  their 
absence  from  other  places  that  are  equally  appropriate  and 
more  appropriate.  Let  us  consider  the  phenomena  under 
these  categories. 

§  105.  Facts  which  illustrate  the  limiting  influence  of  sur- 
rounding conditions,  are  abundant,  and  familiar  to  all  read- 
ers. It  will  be  needful,  however,  here  to  cite  a  few  typical 
ones  of  each  order. 


312  THE    .NDUCT10NS   OF    BIOLOGY. 

The  confinement  of  different  kinds  of  plants  and  different 
kinds  of  animals,  to  the  media  for  which  they  are  severally 
adapted,  is  the  broadest  fact  of  distribution.  We  have  ex- 
tensive groups  of  plants  that  are  respectively  sub-aerial  and 
sub -aqueous  ;  and  of  the  sub-aqueous,  some  are  exclusively 
marine,  while  others  exist  only  in  rivers  and  lakes.  Among 
animals,  we  similarly  find  some  classes  confined  to  the  air 
and  others  to  the  water ;  and  of  the  water-breathers,  some 
are  restricted  to  salt  water  and  others  to  fresh  water.  Less 
familiar  is  the  fact,  that  within  each  of  these  strongly  con- 
trasted media,  there  are  further  wide-spread  limitations.  In 
the  sea,  certain  organisms  exist  only  between  certain  depths, 
while  other  organisms  exist  only  between  other  depths — the 
limpet  within  the  littoral  zone,  and  the  Globigerina  at  the 
bottom  of  the  Atlantic ;  and  on  the  land,  there  are  Floras 
and  Faunas  peculiar  to  low  regions,  and  others  peculiar  to 
high  regions.  Next  we  have  the  well-known  geographical 
limitations,  made  by  climate.  There  are  temperatures  that 
restrict  each  kind  of  organism  between  certain  isothermal 
lines  ;  and  hygrometric  states  that  prevent  the  spread  of 
each  kind  of  organism  beyond  areas  having  a  certain  hu- 
midity or  a  certain  dryness.  Besides  such  general  limita- 
tions, we  find  much  more  special  limitations.  Some  minute 
vegetal  forms  occur  only  in  snow.  Hot  springs  have  their 
peculiar  Infusoria.  The  habitats  of  certain  Fungi  are  mines 
or  other  dark  places.  And  there  are  creatures  unknown  be- 
yond the  water  contained  in  particular  caves.  After 
these  limits  to  distribution  imposed  by  physical  conditions, 
come  limits  of  a  different  class,  imposed  by  the  presence 
or  absence  of  other  organisms.  Obviously,  graminivorous 
animals  are  confined  within  tracts  which  produce  plants  fit 
for  them  to  feed  on.  Large  carnivores  cannot  exist  out  of 
regions  where  there  are  creatures  numerous  enough  and 
large  enough  to  serve  for  prey.  The  requirements  of  the 
sloth,  limit  it  to  certain  forest- covered  spaces ;  and  there  can 
be  no  insectivorous  bats,  where  there  are  no  niffht- flying 


DISTRIBUTION.  313 

insects.  To  these  dependences  of  the  relatively-stiperioT 
organisms  on  the  relatively-inferior  organisms  which  they 
consume,  must  be  added  certain  reciprocal  dependences  of 
the  inferior  on  the  superior.  Mr  Darwin's  inquiries  have 
shown  how  generally  the  fertilization  of  plants  is  due  to  the 
agency  of  insects  ;  and  how  certain  plants,  being  fertilizable 
only  by  insects  of  a  certain  structure,  are  limited  to  regions 
inhabited  by  insects  of  this  structure.  Conversely,  the  spread 
of  organisms  is  often  bounded  by  the  presence  of  particular 
organisms  beyond  the  bounds — either  competing  organisms 
or  organisms  directly  inimical.  A  plant  that  is  fit  for  some 
territory  adjacent  to  its  own,  fails  to  overrun  it,  because  the 
territory  is  pre- occupied  by  some  plant  that  is  its  superior, 
either  in  fertility  or  power  of  resisting  destructive  agencies  ; 
or  else  because  there  lives  in  the  territory  some  mammal 
which  browses  on  its  foliage,  or  bird  which  devours  nearly  all 
its  seeds.  Similarly,  an  area  in  which  animals  of  a  particu- 
lar species  might  thrive,  is  not  colonized  by  them,  because 
they  are  not  fleet  enough  to  escape  some  beast  of  prey  inhab- 
iting this  area  ;  or  because  the  area  is  infested  by  some  in- 
sect which  destroys  them,  as  the  tsetse  destroys  the  cattle  in 
parts  of  Africa.  Yet  another  more  special  series  of 

limitations,  accompanies  parasitism.  There  are  parasitic 
plants  that  flourish  only  on  trees  of  some  few  kinds ;  and 
others  that  have  certain  animals  for  their  habitats — as  the 
fungus  which  is  fatal  to  the  silk-worm,  or  that  which  so 
strangely  grows  out -of  a  New  Zealand  caterpillar.  Of 
animal-parasitism  we  have  various  kinds  :  severally  involv- 
ing their  specialities  of  distribution.  We  have  that  kind  in 
which  one  creature  uses  another  for  pxirposes  of  locomotion ; 
as  the  Chelonobia  uses  the  turtle,  and  as  a  certain  Ac- 
tinia uses  the  shell  inhabited  by  a  hermit-crab.  We  havo 
that  kind  in  which,  one  creature  habitually  accompanies 
another  to  share  its  prey ;  like  the  annelid  which  takes  up 
its  abode  in  the  shell  occupied  by  a  hermit-crab,  and  snatches 
from  the  hermit-crab,  the  morsels  of  food  it  is  eating.  "Wo 
21 


314  THE    INDUCTIONS    OF    BIOLOGY. 

have  again  the  commoner  parasitism  of  the  Epizoa — animals 
which  attach  themselves  to  the  surfaces  of  other  animals,  and 
feed  on  their  juices  or  on  their  secretions.  And  once  more,  we 
have  the  equally  common  parasitism  of  the  E?ilo~oa — creatures 
which  live  within  other  creatures.  Besides  being  restricted 
ill  its  distribution  to  the  bodies  of  the  organisms  it  infests, 
each  species  of  parasite  has  usually  still  narrower  limitations  : 
in  some  cases  the  infested  organisms  furnish  fit  habitats  for 
the  parasites  only  in  certain  regions  ;  and  in  other  cases,  only 
when  in  certain   constitutional  states.  There  are 

various  more  indirect  modes  in  which  the  distributions  of 
organisms  affect  each  other.  Plants  of  particular  kind3  are 
eaten  by  animals,  only  in  the  absence  of  kinds  that  are 
preferred  to  them ;  and  the  prosperity  of  such  plants,  hence 
partly  depends  on  the  presence  of  the  preferred  plants.  Mr 
Bates  has  pointed  out  that  some  South  American  butterflies, 
thrive  in  regions  where  insectivorous  birds  would  else  destroy 
them,  because  they  closely  resemble  butterflies  of  another 
genus  which  are  disliked  by  those  birds.  And  Mr  Darwin 
gives  cases  of  dependence  still  more  remote  and  involved. 

Such  are  the  chief  negative  causes  of  distribution — the 
inorganic  and  organic  agencies,  that  set  bounds  to  the  spaces 
which  organisms  of  each  species  inhabit.  Fully  to  under- 
stand their  actions,  we  must  contemplate  them  as  working 
not  separately,  but  in  concert.  We  have  to  regard  the 
physical  influences,  varying  from  year  to  year,  as  now 
producing  an  extension  or  restriction  of  the  habitat  in  this 
direction,  and  now  in  that ;  and  as  producing  secondary 
extensions  and  restrictions,  by  their  effects  on  other  kinds  of 
organisms.  "We  have  to  regard  the  distribution  of  each 
organism,  not  only  as  affected  by  causes  which  favour  multi- 
plication of  prey  or  of  enemies  within  its  own  area  ;  but  also 
by  causes  which  produce  such  results  in  neighbouring  areas. 
We  have  to  conceive  the  forces  by  which  the  limit  is 
maintained,  as  including  all  meteorologic  influences,  united 


DISTRIBUTION.  315 

with  the  influences,  direct  or  more  or  less  re  mot     of  nearly 
all  co-existing  organisms. 

One  general  truth,  indicated  by  sundry  of  the  above  illus- 
trations, calls  for  special  notice — the  truth  that  organisms 
are  ever  intruding  on  each  other's  spheres  of  existence.  Of 
the  various  modes  in  which  this  is  shown,  the  commonest  is 
the  invasion  of  territory.  That  tendency  which  we  see  in 
the  human  races,  to  overrun  and  occupy  each  other's  lands, 
as  well  as  the  lands  inhabited  by  inferior  creatures,  is  a 
tendency  exhibited  by  all  classes  of  organisms  in  all  va- 
rieties of  ways.  Among  them,  as  among  mankind,  there  are 
permanent  conquests,  temporary  occupations,  and  occasional 
raids.  Annual  migrations  are  instances  of  this  process  in 
its  most  familiar  form.  Every  spring  an  inroad  is  made  into 
the  area  which  our  own  fly-catchers  occupy,  by  the  swallows 
of  the  South  ;  and  every  winter  the  fieldfares  of  the  North, 
come  to  share  the  hips  and  haws  of  our  hedges  with  native 
birds — a  partial  possession  of  their  territory,  which  entails 
on  our  native  birds,  some  mortality.  Besides  these  regularly- 
recurring  raids,  there  are  irregular  ones :  as  of  locusts  into 
countries  not  usually  visited  by  them  ;  or  of  strange  birds 
which  in  small  flocks  from  time  to  time  visit  areas  adjacent 
to  their  own.  Every  now  and  then,  an  incursion  ends  in 
permanent  settlement — perhaps  in  conquest  over  indigenous 
species.  Within  these  few  years,  an  American  water-weed 
has  taken  possession  of  our  ponds  and  rivers,  and  to  some 
extent  supplanted  native  water- weeds.  Of  animals,  may  be 
named  a  small  kind  of  red  ant,  having  habits  allied  to  those 
of  tropical  ants,  which  has  of  late  overrun  many  houses  in 
London.  The  case  of  the  rat,  which  must  have  taken  to 
infesting  ships  within  these  few  centuries,  is  a  good  illustra- 
tion of  the  readiness  of  animals  to  occupy  new  places  that 
are  available.  And  the  way  in  which  vessels  visiting  India, 
are  cleared  of  the  European  cockroach  by  the  kindred  Blatta 
orientaJis,  shows  us  how  these  successful  invasions  last  only 
until  there  come  more  powerful  invaders.  Organ 


316  THE    INDUCTIONS   OF    BIOLOGY. 

isms  encroach  on  one  another's  spheres  of  existence,  in  fur- 
ther ways  than  by  trespassing  on  one  another's  areas  :  they 
adopt  one  another's  modes  of  life.  There  are  cases  in  which 
this  usurpation  of  habits  is  slight  and  temporary  ;  and  there 
are  cases  where  it  is  marked  and  permanent.  Grey  crows 
frequently  join  gulls  and  curlews  in  picking  up  food  between 
tide-marks  ;  and  gulls  and  curlews  may  be  occasionally  seen 
many  miles  inland,  feeding  in  ploughed  fields  and  on  moors. 
Mr  Darwin  has  watched  a  fly-catcher  catching  fish.  lie 
says  that  the  greater  titmouse  sometimes  adopts  the  practices 
of  the  shrike,  and  sometimes  of  the  nuthatch  ;  and  that  some 
South  American  woodpeckers  are  frugivorous,  while  others 
chase  insects  on  the  wing.  Of  habitual  intrusions  on  the 
occupations  of  other  creatures,  one  case  is  furnished  by  the 
sea-eagle  ;  which,  besides  hunting  the  surface  of  the  land  for 
prey,  like  the  rest  of  the  hawk-tribe,  often  swoops  down  upon 
fish.  And  Mr  Darwin  names  a  species  of  petrel  that  has 
taken  to  diving,  and  has  a  considerable,  modified  organiza- 
tion. These  last  cases  introduce  us  to  a  still  more 
remarkable  class  of  facts  of  kindred  meaning.  This  intrusion 
of  organisms  on  one  another's  modes  of  life,  goes  to  the  ex- 
tent of  intruding  on  one  another's  media.  The  great  mass 
of  flowering  plants  are  terrestrial ;  and  are  required  to  be  so 
by  their  process  of  fructification.  But  there  are  some  which 
live  in  the  water,  and  protrude  only  their  flowers  above  the 
surface.  Nay,  there  is  a  still  more  striking  instance :  on  the 
sea-shore  may  be  found  an  alga  a  hundred  yards  inland, 
and  a  phsenogam  rooted  in  salt-water.  Among  animals, 
these  interchanges  of  media  are  numerous.  Nearly  all 
coleopterous  "insects  are  terrestrial;  but  the  water-beetle, 
which  like  the  rest  of  its  order  is  an  air-breather,  has 
aquatic  habits.  Water  appears  to  be  an  especially  uufit 
medium  for  a  fly ;  and  yet  Mr  Lubbock  has  lately  dis- 
covered more  than  one  species  of  fly  living  beneath  the  sur- 
face of  the  water,  and  coming  up  only  occasionally  for  aii. 
Birds,  as  a  class,  are  especially  fitted  for  an  aerial  existence  j 


DISTRIBUTION.  317 

buc  certain  tribes  of  them  have  taken  to  an  aquatic  existence 
— swimming  on  the  surface  of  the  water  and  making  continual 
incursions  beneath  its  surface  ;  and  there  are  some  genera 
that  have  wholly  lost  the  power  of  flight.  Among  mam- 
mals, too,  which  have  limbs  and  lungs  implying  an  organiza- 
tion for  terrestrial  life,  may  be  named  kinds  that  live  more 
or  less  in  the  water,  and  are  more  or  less  adapted  to  it.  We 
have  water-rats  and  otters,  which  unite  the  two  kinds  of  life, 
and  show  but  little  modification  ;  hippopotami  passing  the 
greater  part  of  their  time  in  the  water,  and  somewhat  more 
fitted  to  it;  seals  living  almost  exclusively  in  the  sea,  and 
having  the  mammalian  form  greatly  obscured ;  whales 
wholly  confined  to  the  sea,  and  having  so  little  the  aspect  of 
mammals  as  to  be  mistaken  for  fish.  Conversely,  sundry 
inhabitants  of  the  water  make  more  or  less  prolonged  ex- 
cursions on  the  land.  Eels  migrate  at  night  from  one  pool 
to  another.  There  are  fish  with  specially-modified  gills,  and 
fin-rays  serving  as  stilts,  which,  when  the  rivers  they  in- 
habit are  partially  dried-up,  travel  in  search  of  better  quarters 
And  while  some  kinds  of  crabs  do  not  make  land-excursions 
beyond  high-water  mark,  other  kinds  pursue  lives  almost 
wholly  terrestrial. 

Joining  together  these  two  classes  of  facts,  we  must  regard 
the  bounds  to  each  species'  sphere  of  existence,  as  determined 
by  the  balancing  of  two  antagonist  sets  of  forces.  The  tend- 
ency which  every  species  has  to  intrude  on  other  areas, 
other  modes  of  life,  and  other  media,  is  restrained  by  the 
direct  and  indirect  resistance  of  conditions,  organic  and  inor- 
ganic. And  these  expansive  and  repressive  energies,  vary- 
ing continually  in  their  respective  intensities,  "rhythmically 
equilibrate  each  other — maintain  a  limit  that  perpetually 
oscillates  from  side  to  side  of  a  certain  mean. 

§  106.  As  implied  at  the  outset,  the  character  of  a  region, 
when  unfavourable  to  any  species,  sufficiently  accounts  for  the 
absence  of  this  species ;  and  thus  its  absence  is  not  incon- 


#18  THE    INDUCTI0N3   OF    BIOLOGY. 

gruous  with  the  hypothesis,  that  each  species  was  originally 
placed  in  the  regions  most  favourable  to  it.  But  the  absence 
of  a  species  from  regions  that  are  favourable  to  it,  cannot  be 
thus  accounted  for.  Were  plants  and  animals  localized  wholly 
with  reference  to  the  fitness  of  their  constitutions  to  surround- 
ing conditions,  we  might  expect  Floras  to  be  similar  and 
Faunas  to  be  similar,  where  the  conditions  are  similar  ;  and 
we  might  expect  dissimilarities  among  Floras  and  among 
Faunas,  proportionate  to  the  dissimilarities  of  their  conditions. 
But  we  do  not  find  such  anticipations  verified. 

Mr  Darwin  says  that  "  in  the  Southern  hemisphere,  if  we 
compare  large  tracts  of  land  in  Australia,  South  Africa,  and 
western  South  America,  between  latitudes  25°  and  35°,  we  shal- 
find  parts  extremely  similar  in  all  their  conditions,  yet  it 
would  not  be  possible  to  point  out  three  faunas  and  floras 
more  utterly  dissimilar.  Or  again  we  may  compare  the  pro- 
ductions of  South  America  south  of  lat.  35°  with  those  north 
of  25°,  which  consequently  inhabit  a  considerably  different  cli- 
mate, and  they  will  be  found  incomparably  more  closely  related 
to  each  other,  than  they  are  to  the  productions  of  Australia 
or  Africa  under  nearly  the  same  climate."  Still  more  striking 
are  the  contrasts  which  Mr  Darwin  points  out,  between  closely- 
adjacent  areas  that  are  totally  cut-off  from  each  other.  "  No 
two  marine  faunas  are  more  distinct,  with  hardly  a  fish,  shell, 
or  crab  in  common,  than  those  of  the  eastern  and  western 
shores  of  South  and  Central  America  ;  yet  these  great  faunas 
are  separated  only  by  the  narrow,  but  impassable,  isthmus  of 
Panama."  On  opposite  sides  of  high  mountain-chains,  also, 
there  are  marked  differences  in  the  organic  forms — differ- 
ences not  so  marked  as  where  the  barriers  are  absolutely  im- 
passable ;  but  much  more  marked  than  are  necessitated  b}' 
unlikenesses  of  physical  conditions. 

Not  less  suggestive  is  the  converse  fact,  that  wide  geogra- 
phical areas  which  offer  decided  geologic  and  meteorologic 
contrasts,  are  peopled  by  nearly-allied  groups  of  organisms,  if 
there  are  no  barriers  to  migration.     "  The  naturalist  in  tra- 


DISTRIBUTION.  319 

veiling,  for  instance,  from  north  to  south  never  fails  to  be 
Btruck  by  the  manner  in  which  successive  groups  of  beings, 
specifically  distinct,  yet  clearly  related,  replace  each  other. 
He  hears  from  closely  allied,  )Tet  distinct  kinds  of  birds, 
notes  nearly  similar,  and  sees  their  nests  similarly  constructed, 
but  not  quite  alike,  with  eggs  coloured  in  nearly  the  same 
manner.  The  plains  near  the  Straits  of  Magellan  are  inhabit- 
ed by  one  species  of  Rhea  (American  Ostrich),  and  north-ward 
the  plains  of  La  Plata  by  another  species  of  the  same  genus ; 
and  not  by  a  true  ostrich  or  emeu,  like  those  found  in  Africa 
and  Australia  under  the  same  latitude.  On  these  same  plains 
of  La  Plata,  we  see  the  agouti  and  bizcacha,  animals  having 
nearly  the  same  habits  as  our  hares  and  rabbits  and  belonging 
to  the  same  order  of  Rodents,  but  they  plainly  display  an 
American  type  of  structure.  "We  ascend  the  lofty  peaks  of 
the  Cordillera  and  we  find  an  alpine  species  of  bizcacha ;  wre 
took  to  the  waters,  and  we  do  not  find  the  beaver  or  musk- 
rat,  but  the  coypu  and  capybara,  rodents  of  the  American 
type.  Innumerable  other  instances  could  be  given.  If  we 
look  to  the  islands  off  the  American  shore,  however  much 
they  may  differ  in  geological  structure,  the  inhabitants,  though 
they  may  be  all  peculiar  species,  are  essentially  American." 

TVhatisthe  generalization  that  expresses  these  two  groups 
of  facts  ?  On  the  one  hand,  wTe  have  similarly-conditioned, 
and  sometimes  nearly- adjacent,  areas,  occupied  by  quite  dif- 
ferent Faunas.  On  the  other  hand,  we  have  areas  remote  from 
each  other  in  latitude,  and  contrasted  in  soil  as  well  as  climate, 
which  are  occupied  by  closely-allied  Faunas.  Clearly  then,  as 
like  organisms  are  not  universally,  or  even  generally,  found 
in  like  habitats  ;  nor  very  unlike  organisms,  in  very  unlike 
habitats ;  there  is  no  manifest  pre-determined  adaptation  of 
the  organisms  to  the  habitats.  The  organisms  do  not  occur 
in  such  and  such  places,  solely  because  they  are  either  spe- 
cially fit  for  these  places,  or  more  fit  for  them  than  all  other 
organisms. 

The  induction   under  which  these  facts  come,  and  whiel; 


o20  THE    INDUCTIONS    OF    BIOLOGY. 

unites  tliera  with  various  other  facts,  is  a  totally-different  one. 
When  we  see  that  the  similar  areas  peopled  by  dissimilar 
forms,  are  those  between  which  there  are  impassable  barriers ; 
while  the  dissimilar  areas  peopled  by  similar  forms,  are  those 
between  which  there  are  no  such  barriers  ;  we  are  at  once  re- 
minded of  the  general  truth  exemplified  in  the  last  section : — 
the  truth  that  each  species  of  organism,  tends  ever  to  expand 
its  sphere  of  existence — to  intrude  on  other  areas,  other 
modes  of  life,  other  media ;  and  through  these  perpetually- 
recurring  attempts  to  thrust  itself  into  every  accessible  habitat, 
spreads  until  it  reaches  limits  that  are  for  the  time  insur- 
mountable. 

§  107.  We  pass  now  to  the  distribution  of  organic  forms 
in  Time.  Geological  inquiry  has  established  the  truth,  that 
during  a  Past  of  immeasurable  duration,  plants  and  animals 
have  existed  on  the  Earth.  In  all  countries  their  buried 
remains  are  found  in  greater  or  less  abundance.  From  com- 
paratively small  areas,  multitudinous  different  forms  have  been 
exhumed.  Every  exploration  of  new  areas,  and  every  closer 
inspection  of  areas  already  explored,  brings  more  such  forms 
to  light.  And  beyond  question,  an  exhaustive  examination  of 
all  exposed  strata,  and  of  all  strata  now  covered  by  the  sea, 
would  disclose  forms  immensely  out-numbering  all  those  at 
present  known.  Further,  it  is  now  becoming  manifest  to 
geologists,  that  even  had  Ave  before  us  every  kind  of  fossil 
which  exists,  we  should  still  have  nothing  like  a  complete 
index  to  the  past  inhabitants  of  our  globe.  It  has  been  long 
known  that  many  sedimentary  deposits  have  been  so  altered 
by  the  heat  of  adjacent  molten  matter,  as  greatly  to  obscure 
the  organic  remains  contained  in  them.  The  extensive  form- 
ations once  called  "  transition,"  and  now  re-named  "  meta- 
m orphic,"  are  acknowledged  to  be  formations  of  sedimentary 
origin,  from  which  all  traces  of  such  fossil  as  they  probably 
included,  have  been  obliterated  by  igneous  action.  And  the 
conclusion  forcing  itself  into  acceptance,  is,  that  igneous  rock 


DISTRIBUTION.  321 

haa  everywhere  resulted  from  tlie  complete  melting-up  oi 
beds  of  detritus,  originally  deposited  by  water.  How  long  the 
reactions  of  the  Earth's  molten  nucleus  on  its  cooled  crust, 
have  been  thus  destroying  the  records  of  Life  which  this  cooled 
crust  entombed,  it  is  impossible  to  say  ;  but  there  are  strong 
reasons  for  believing  that  the  records  which  remain,  bear  but, 
n  small  ratio  to  the  records  which  have  been  destroyed.  Thus 
we  have  but  extremely-imperfect  data  for  any  conclusions 
respecting  the  distribution  of  organic  forms  in  Time.  Sonio 
few  generalizations,  however,  may  be  regarded  as  established. 

One  is,  that  the  plants  and  animals  now  existing,  mostly 
differ  from  the  plants  and  animals  which  have  existed. 
Though  there  are  species  common  to  our  present  Fauna  and 
to  past  Faunas  ;  yet  the  fades  of  our  present  Fauna  differs, 
more  or  less,  from  the  fades  of  each  past  Fauna.  On  carry- 
ing out  the  comparison,  we  find  that  past  Faunas  differ  from 
each  other ;  and  that  the  differences  between  them  are  pro- 
portionate to  their  degrees  of  remoteness  from  each  other  in 
Time,  as  measured  by  their  relative  positions  in  the  sediment- 
ary series.  So  that  if  we  take  the  assemblage  of  organic 
forms  living  now,  and  compare  it  with  the  successive  assem- 
blages of  organic  forms  that  have  lived  in  successive  geologic 
epochs,  we  find  that  the  farther  we  go  back  into  the  past,  the 
greater  does  the  unlikeness  become  :  the  number  of  species 
and  genera  common  to  the  compared  assemblages,  becomes 
smaller  and  smaller  ;  and  the  assemblages  differ  more  and 
more  in  their  general  characters.  Though  a  species  of 
brachiopod  now  extant,  is  almost  identical  with  a  species 
found  in  Silurian  strata,  and  though  between  the  Silurian 
Fauna  and  our  own,  there  are  sundry  common  genera  of  mol- 
luscs ;  it  is  still  undeniable  that  there  is  a  proportion  between 
lapse  of  time  and  divergence  of  organic  forms. 

This  divergence  is  comparatively  slow  and  continuous 
where  there  is  continuity  in  the  geological  formations  ;  but  is 
sudden  and  comparatively  wide,  wherever  there  occurs  a 
groat  break  in  the  succession  of  strata.     The  contrasts  which 


'622  THE    INDUCTIONS    OF    BIOLOGY. 

thus  arise  gradually  or  all  at  once,  in  formations  that  are 
continuous  or  discontinuous,  are  of  two  kinds.  Faunas  of 
different  eras,  are  distinguished  partly  by  the  absence  from 
one  of  types  that  are  present  in  the  other ;  and  partly  by  the 
unlikenesses  between  the  types  that  are  common  to  both. 
Such  distinctions  between  Faunas  as  are  due  to  the  appear- 
ance or  disappearance  of  types,  are  of  secondary  significance : 
they  possibly,  or  probably,  do  not  imply  anything  more  than 
migrations  or  extinctions.  The  most  significant  distinctions 
are  those  between  successive  groups  of  organisms  of  the  same 
type.  And  among  such,  as  above  said,  the  differences  that 
arise  are,  speaking  generally,  small  and  continuous  where  a 
series  of  conformable  strata  gives  proof  of  continued  existence 
of  the  type  in  the  locality  :  while  they  are  comparatively 
large  and  abrupt,  where  there  is  evidence  that  between  the 
deposit  of  the  adjacent  formations,  a  long  period  elapsed. 

Another  general  fact,  referred  to  by  Mr  Darwin  as  one 
which  palaeontology  has  made  tolerably  certain,  is  that  forms 
and  groups  of  forms  which  have  once  disappeared  from  the 
Earth,  do  not  reappear.  Some  few  species  and  a  good  many 
genera,  have  continued  throughout  the  whole  period  geologi- 
cally recorded.  But  omitting  these  as  exceptional,  it  may  be 
said  that  each  species  after  arising,  spreading  for  an  era,  and 
continuing  abundant  for  an  era,  eventually  declines  and  be- 
comes extinct ;  and  that  similarly,  each  genus  during  a  longer 
period  increases  in  the  number  of  its  species,  and  during  a 
longer  period  dwindles  and  at  last  dies  out.  Having  made 
its  exit,  neither  species  nor  genus  ever  re-enters.  And  the 
like  is  true,  even  of  those  larger  groups  called  orders.  Four 
tvpes  of  reptiles  that  were  once  abundant,  have  not  been 
found  in  modern  formations,  and  do  not  at  present  exist. 
Though  nothing:  less  than  an  exhaustive  examination  of  all 
strata,  can  prove  conclusively  that  a  special  or  general  form  of 
organization  when  once  lost  is  never  reproduced  ;  yet  so 
many  facts  point  to  this  inference,  that  its  truth  can  scarcely 
be  doubted. 


DISTRIBUTION.  ?>23 

To  form  a  conception  of  the  total  amount  and  general 
direction  of  the  change  that  has  arisen  in  organic  forms  during 
the  geologic  time  measured  by  our  sedimentary  series,  is  at 
present  impossible — the  data  are  insufficient.  The  immense 
contrast  between  the  few  and  low  forms  of  the  earliest-known 
Fauna,  and  the  many  and  high  forms  of  our  existing  Fauna, 
has  been  commonly  supposed  to  prove,  not  only  great 
change  but  great  progress.  Nevertheless,  this  appearance 
of  progress  may  be,  and  prob.ibly  is,  mainly  illusive. 
Wider  knowledge  and  increased  power  of  interpretation,  have 
made  it  manifest  that  remains  of  comparative^  well-organized 
creatures,  really  existed  in  strata  long  supposed  to  be  devoid 
of  them  ;  and  that  where  they  are  actually  absent,  the  nature 
of  the  strata  often  supplies  a  sufficient  explanation  of  their 
absence,  without  assuming  that  they  did  not  exist  when  these 
strata  were  formed.  It  has  now  become  a  tenable  hypothesis, 
that  the  successively-higher  types  fossilized  in  our  successive- 
ly-later deposits,  indicate  nothing  more  than  successive  migra- 
tions from  pre-existing  continents,  to  continents  that  were 
step  by  step  emerging  from  the  ocean — migrations  which 
necessarily  began  with  the  inferior  orders  of  organisms,  and 
included  the  successively-superior  orders  as  the  new  lands 
became  more  accessible  to  them,  and  better  fitted  for  them.* 

While  the  evidence  usually  supposed  to  prove  progres- 
sion, is  thus  untrustworthy,  there  is  trustworthy  evidence 
that  there  has  been,  in  many  cases,  little  or  no  progression. 
Though  the  types  which  have  existed  from  pakeozoic  and  me- 
sozoic  times  clown  to  the  present  day,  are  almost  universally 
changed  ;  yet  a  comparison  of  ancient  and  modern  members 
of  these  types,  shows  that  the  total  amount  of  change  is  not 
relatively  great,  and  that  it  is  not  manifestly  towards  a  higher 
organization.  Though  nearly  all  the  living  forms  which  have 
prototypes  in  early  formations,  differ  from  these  prototypes 
specifically,  and  in  most  cases  generically  ;  yet  ordinal  pecu- 
liarities are,  in  very  numerous  cases,  maintained  from  the  earli- 

*  For  explanations,  sec  "Illogical  Geology."    Essays:  Second  Series. 


824  TUE   INDUCTIONS   OF   BIOLOGY. 

est  times  geologically  recorded,  down  to  our  own  time ;  and  we 
have  no  visible  evidence  of  superiority  in  the  existing  genera 
of  these  orders.  In  his  lecture  "  On  the  Persistent  Types  of 
Animal  Life,"  Prof.  Huxley  enumerates  many  cases.  On 
the  authority  of  Dr.  Hooker,  he  stated  "  that  there  are  Carbon- 
iferous plants  which  appear  to  be  generically  ideutical  with 
some  now  living  ;  that  the  cone  of  the  Oolitic  Araucaria  is 
hardily  distinguishable  from  that  of  an  existing  species ;  that  a 
true  Pinu8  appears  in  the  Purbecks  and  a  Juglans  in  the 
chalk."  Among  animals  he  named  palaeozoic  and  mesozoic 
corals  which  are  very  like  certain  extant  corals ;  genera  of  Silu- 
rian molluscs  that  answer  to  existing  genera ;  insects  and  arach- 
nids in  the  coal  formations,  that  are  not  more  than  generically 
different  from  some  of  our  own  insects  and  arachnids.  He 
instanced  "  the  Devonian  and  Carboniferous  Pleur acanthus, 
which  differs  no  more  from  existing  sharks  than  these  do 
from  one  another ; "  early  mesozoic  reptiles  "  identical  in  the 
essential  characters  of  their  organization  with  those  now  liv- 
ing ; "  and  Triassic  mammals  which  did  not  differ  "  nearly  so 
much  from  some  of  those  which  now  live,  as  these  differ  from 
one  another."  Continuing  the  argument  in  his  "  Anniversary 
x\ddresa  to  the  Geological  Society "  in  1862,  Prof.  Huxley 
gave  many  cases  in  which  the  changes  that  have  taken  place, 
are  not  changes  towards  a  more  specialized  or  higher  organ- 
ization— asking  "  in  what  sense  are  the  Liassic  Chelonia  infe- 
rior to  those  which  now  exist  %  How  are  the  Cretaceous 
Ichthyosauria,  Plesiosauria,  or  Pterosauria  less  embryonic 
or  more  differentiated  species  than  those  of  the  Lias  ? " 
While,  however,  contending  that  in  most  instances  "  positive 
evidence  fails  to  demonstrate  any  sort  of  progressive  modifi- 
cation towards  a  less  embryonic  or  less  generalized  type  in  a 
great  many  groups  of  animals  of  long-continued  geological 
existence ; "  Prof.  Huxley  added,  that  there  are  other  groups 
"  co-existing  with  them,  under  the  same  conditions,  in  which 
more  or  less  distinct  indications  of  such  a  process  seem  to  be 
traceable."    And  in  illustration  of  this,  he  named  that  better 


distribi  t:on.  325 

development  of  the  vertebne  which  characterizes  some  of 
the  more  modern  fishes  and  reptiles,  when  compared  with  an- 
cient fishes  and  reptiles  of  the  same  orders  ;  and  the  "  regu- 
larity and  evenness  of  the  dentition  of  the  Ajiojplothertum 
as  contrasting  with  that  of  existing  Artiodactyles." 

The  facts  thus  summed  up,  do  not  show  that  higher  forms 
have  not  arisen  on  the  Earth  in  the  course  of  geologic  time, 
any  more  than  the  facts  commenly  cited  prove  that  higher 
forms  have  arisen  ;  nor  are  they  regarded  by  Prof.  Huxley 
as  showing  this.  "Were  the  types  which  have  survived  from 
palaeozoic  and  mesozoic  periods  down  to  our  own  day,  the 
only  types ;  and  did  the  modifications,  rarely  of  more  than 
generic  value,  which  these  types  have  undergone,  give  no 
better  evidences  of  increase1  complexity  than  are  actually 
given  by  them ;  then  it  would  bt  inferable  that  there  has 
been  no  appreciable  advance  among  organic  forms.  But 
there  now  exist,  and  have  existed  during  the  more  recent 
geologic  epochs,  various  types  which  are  not  known  to  have 
existed  in  earlier  epochs  —  some  of  them  widely  unlike 
these  persistent  types,  and  some  of  them  nearly  allied  to 
these  persistent  types.  As  yet,  we  know  nothing  respecting 
the  origins  of  these  new  types.  But  it  is  quite  possible  that 
causes  like  those  which  have  produced  generic  differences  in 
the  persistent  types,  may,  in  some  or  many  cases,  have  pro- 
duced modifications  great  enough  to  constitute  ordinal  differ- 
ences— may  have  resulted  in  the  formation  of  types  that  are 
now  classed  as  separate.  If  structural  contrasts  not  exceed- 
ing certain  moderate  limits,  are  held  to  mark  only  generic 
distinctions ;  and  if  organisms  displaying  larger  structural 
contrasts  are  considered  ordinally  or  typically  distinct ;  it  is 
dear  that  the  persistence  of  a  given  type  through  a  long 
geologic  period  without  apparently  undergoing  deviations  of 
more  than  generic  value,  by  no  means  disproves  the  occurrence 
of  far  greater  deviations ;  since  the  forms  resulting  from  such 
far  greater  deviations,  being  regarded  as  typically  distinct 
forms,  will  not  be  taken  as  evidence  of  great  change  in  the 


326  THE    INDUCTIONS   OF   BIOLOGY. 

original  type.  That  which.  Prof.  Huxley's  argument  proves, 
and  that  only  which  he  considers  it  to  prove,  is  that  organisms 
have  no  innate  tendencies  to  assume  higher  forms,  and  that 
"  any  admissible  hypothesis  of  progressive  modification,  must 
be  compatible  with  persistence  without  progression  through 
indefinite  periods." 

One  very  significant  fact  must  be  added,  concerning  the 
relation  between  distribution  in  Time  and  distribution  in 
Space.  I  quote  it  from  Mr  Darwin  : — "  Mr  Clift  many  years 
ago  showed  that  the  fossil  mammals  from  the  Australian 
caves  were  closely  allied  to  the  living  marsupals  of  that  con- 
tinent. In  South  America,  a  similar  relationship  is  manifest 
even  to  an  uneducated  eye,  in  the  gigantic  pieces  of  armour 
like  those  of  the  armadillo,  found  in  several  parts  of  La  Plata ; 
and  Professor  Owen  has  shown  in  the  most  striking  manner 
that  most  of  tie  fossil  mammals,  buried  there  in  such  num- 
bers, are  related  to  the  South  American  types.  This  relation- 
ship is  even  more  clearly  seen  in  the  wonderful  collection  of 
fossil  bones  made  by  MM.  Lund  and  Clausen  in  the  caves  of 
Brazil.  I  was  so  much  impressed  with  these  facts  that  I 
strongly  insisted,  in  1839  and  1845,  on  this  '  law  of  the  suc- 
cession of  types/ — on  '  this  wonderful  relationship  in  the 
same  continent  between  the  dead  and  the  living.'  Professor 
Owen  has  subsequently  extended  the  same  generalization  to  the 
mammals  of  the  Old  World.  We  see  the  same  law  in  this 
author's  restorations  of  the  extinct  and  gigantic  birds  of  New 
Zealand.  We  see  it  also  in  the  birds  of  the  caves  of  Brazil. 
Mr  Woodward  has  shown  that  the  same  law  holds  good,  with 
sea-shells,  but  from  the  wide  distribution  of  most  genera  of 
molluscs,  it  is  not  well  displayed  by  them.  Other  cases  could 
be  added,  as  the  relation  between  the  extinct  and  living  land- 
fihells  of  Madeira  ;  and  between  the  extinct  and  living  brack- 
ish-water shells  of  the  Aralo-Caspian  Sea.'" 

The  general  results  then,  are  these.  Our  knowledge  of 
distribution  in  Time,  being  derived  wholly  from  the  evidence 
afforded  by  fossils,  is  limited  to  that  geologic  time  of  which 


DISTRIBUTION.  327 

some  records  remain  :  cannot  extend  to  those  pre-geologic 
times  the  records  of  which  have  been  obliterated.  From 
these  remaining  records,  which  probably  form  but  a  small 
fraction  of  the  whole,  the  general  facts  deducible  are  : — That 
such  organic  types  as  have  lived  through  successive  epochs, 
have  almost  universally  undergone  modifications  of  specific 
and  generic  values — modifications  which  have  commonly  been 
great  in  proportion  as  the  period  has  been  long.  That  besides 
the  types  that  have  persisted  from  ancient  eras  down  to  our 
own  era,  other  types  have  from  time  to  time  made  their  ap- 
pearance in  the  ascending  series  of  our  strata — types  of  which 
some  are  lower  and  some  higher  than  the  types  previously 
recorded  ;  but  whence  these  new  types  came,  and  whether 
anj  of  them  arose  by  divergence  from  the  previously-recorded 
types,  the  evidence  does  not  yet  enable  us  to  say.  That  in 
the  course  of  long  geologic  epochs,  nearly  all  species,  most 
gerera,  and  a  few  orders,  become  extinct ;  and  that  a  species, 
genus,  or  order,  which  has  once  disappeared  from  the  Earth, 
never  reappears.  And,  lastly,  that  the  Fauna  now  occupying 
each  separate  area  of  the  Earth's  surface,  is  very  nearly  allied 
to  the  Fauna  which  existed  on  that  area  during  recent  geolo 
gic  times. 

§  108.  Omitting  sundry  minor  generalizations,  the  exposi- 
tion of  which  would  involve  too  much  detail,  what  is  to  be 
said  of  these  major  generalizations  ? 

The  distribution  in  Space  cannot  be  said  to  imply  that  or- 
ganisms have  been  designed  for  their  particular  habitats,  and 
placed  in  them  ;  since,  besides  the  habitat  in  which  an  organ- 
ism is  found  there  are  commonly  other  habitats,  as  well  or 
better  for  it,  from  which  it  is  absent — habitats  to  which  it 
is  so  much  better  fitted  than  organisms  now  occupying  them, 
that  it  extrudes  these  organisms  when  allowed  the  oppor- 
tunity. Neither  can  we  suppose  that  one  end  has  been  to 
establish  varieties  of  Floras  and  Faunas  ;  since,  if  so,  why  are 
the  Floras  and  Faunas  but  little  divergent  in  widely-sundered 


328  THE    INDUCTIONS    OF    BIOLOGY. 

areas  between  which  migration  is  possible,  while  they  are 
markedly  divergent  in  adjacent  areas  between  which  migra- 
tion is  impossible  ? 

Passing  to  distributions  in  Time,  there  arise  the  questions 
— why  during  nearly  the  whole  of  that  vast  period  geological- 
ly recorded,  have  there  existed  none  of  those  highest  organic 
forms  which  have  now  overrun  the  Earth  ? — how  is  it  that  we 
find  no  traces  of  a  creature  endowed  with  large  capacities  for 
knowledge  and  happiness  ?  The  answer  that  the  Earth  was 
not,  in  remote  times,  a  fit  habitation  for  such  a  creature,  be- 
sides being  unwarranted  by  the  evidence,  suggests  the  equally 
awkward  question — why  during  untold  millions  of  j^earsdid  the 
Earth  remain  fit  only  for  inferior  creatures  ?  What,  again,  is 
the  meaning  of  this  extinction  of  types  ?  To  conclude  that 
the  saurian  type  was  replaced  by  other  types  at  the  beginning 
of  the  tertiary  period,  because  this  type  was  not  adapted  to 
the  conditions  which  then  arose,  is  to  conclude  that  this  type 
could  not  be  modified  into  fitness  for  the  conditions  ;  and  this 
conclusion  is  quite  at  variance  with  the  hypothesis  that  creative 
skill  is  shown  in  the  multiform  adaptations  of  one  type  to 
many  ends. 

What  interpretations  may  rationally  be  put  on  these  and 
other  general  facts  of  distribution  in  Space  and  Time,  we 
shall  see  in  the  next  division  of  this  work ;  to  which  le*  lie 
now  pass 


PART    III. 


THE   EVOLUTION   OF   LIFE, 


22 


CHAPTER   I. 

PRELIMINARY. 

§  109.  In  the  foregoing  Part,  we  have  contemplated  the 
most  important  of  the  generalizations  to  which  biologists 
have  been  led  by  observation  of  organisms.  These  Induc- 
tions of  Biology  have  also  been  severally  glanced  at  on  their 
deductive  sides ;  for  the  purpose  of  noting  the  harmony  that 
exists  between  them,  and  those  primordial  truths  set  forth  in 
First  Principles.  Having  thus  studied  the  leading  pheno- 
mena of  life  separately,  we  are  prepared  for  studying  them  in 
their  ensemble,  with  the  view  of  arriving  at  the  most  general 
interpretation  of  them. 

There  is  an  ensemble  of  vital  phenomena  presented  by  each 
organism  in  the  course  of  its  growth,  development,  and  decay ; 
and  there  is  an  ensemble  of  vital  phenomena  presented  by 
the  organic  world  as  a  whole.  Neither  of  these  can  be 
properly  dealt  with  apart  from  the  other.  But  the  last  of 
them  may  be  separately  treated  more  conveniently  than  the 
first.  What  interpretation  we  put  on  the  facts  of  structure 
and  function  in  each  living  body,  depends  entirely  on  our 
conception  of  the  mode  in  which  living  bodies  in  general 
have  originated.  To  form  some  conclusion  respecting  this 
mode — a  provisional  if  not  a  permanent  conclusion — must 
therefore  be  our  first  slop. 

A\re  have  to  choose  between  two  hypotheses — the  hypo- 
thesis of  Special  Creation  and  the  hypothesis  of  Evolution. 


332  THE    EVOLUTION    OF    LIFE. 

Either  the  multitudinous  kinds  of  organisms  that  now  exist, 
and  the  still  more  multitudinous  kinds  that  have  existed 
during  past  geologic  eras,  have  been  from  time  to  time  separ- 
ately made ;  or  they  have  arisen  by  insensible  steps,  through 
actions  such  as  we  see  habitually  going  on.  Both  hypo- 
theses imply  a  Cause.  The  last,  certainly  as  much  as  the 
first,  recognizes  this  Cause  as  inscrutable.  The  point  at, 
issue  is,  how  this  inscrutable  Cause  has  worked  in  the  pro 
Auction  of  living  forms.  This  point,  if  it  is  to  be  decided  at 
all,  is  to  be!  decided  only  by  examination  of  evidence.  Lot 
us  inquire  which  of  these  antagonist  hypotheses  is  most  con- 
gruous with  established  facts. 


CHAPTER   II. 
GENERAL  ASPECTS  OF   THE    SPECTAL-CHEATIOX-IIYPOTHESIS* 

§  110.  Early  ideas  are  not  usually  true  ideas.  Unde- 
veloped intellect,  be  it  that  of  an  individual  or  that  of  the 
race,  forms  conclusions  which  require  to  be  revised  and  re- 
revised,  before  they  reach  a  tolerable  correspondence  with 
realities.  Were  it  otherwise,  there  would  be  no  discovery, 
no  increase  of  intelligence.  What  we  call  the  progress  of 
knowledge,  is  the  bringing  of  Thoughts  into  harmony  with 
Things ;  and  it  implies  that  the  first  Thoughts  are  either 
wholly  out  of  harmony  with  Things,  or  in  very  incomplete 
harmony  with  them. 

If  illustrations  be  needed,  the  history  of  every  science 
furnishes  them.  The  primitive  notions  of  mankind  as  to  the 
structure  of  the  heavens,  were  wrong ;  and  the  notions 
which  replaced  them  were  successively  less  wrong.  The 
original  belief  respecting  the  form  of  the  Earth  was  wrong  ; 
and  this  wrong  belief  survived  through  the  first  civilizations. 
The  earliest  ideas  that  have  come  down  to  us  concerning  the 
natures  of  the  elements  were  wrong;  and  only  in  quite 
recent  times  has  the  composition  of  matter  in  its  various 
forms  been  bettei  understood.  The  interpretations  of  me- 
chanical facts,  of  meteorological  facts,  of  physiological  facts, 

*  Several  of  the  ar^umeuts  used  in  this  chapter  and  in  that  which  follows  it, 
formed  parts  of  an  essay  on  "the  Development  Hypothesis,"  originally  published 
in  1852 


334  THE    EVOLUTION    OF    LIFE. 

wore  at  first  wrong.  In  all  these  cases  men  set  out  with 
beliefs  which,  if  not  absolutely  false,  contained  but  small 
amounts  of  truth  disguised  by  immense  amounts  of  error. 

Hence  the  hypothesis  that  living  beings  resulted  from 
special  creations,  being  a  primitive  hypothesis,  is  probably 
an  untrue  hypothesis.  If  the  interpretations  of  Nature  given 
b}r  aboriginal  men,  were  erroneous  in  other  directions,  they 
were  most  likely  erroneous  in  this  direction.  It  would  be 
strange  if,  while  these  aboriginal  men  failed  to  reach  the  truth 
in  so  many  cases  where  it  is  comparatively  conspicuous, 
they  yet  reached  the  truth  in  a  case  where  it  is  compara- 
tively hidden. 

§  111.  Besides  the  improbability  given  to  the  belief  in 
special  creations,  by  its  association  with  mistaken  early 
beliefs  in  general ;  a  further  improbability  is  given  to  it  by 
its  association  with  a  special  class  of  mistaken  beliefs.  It 
belongs  to  a  family  of  beliefs  which  have  one  after  another 
been  destroyed  by  advancing  knowledge ;  and  is,  indeed, 
almost  the  only  member  of  the  family  that  survives  among 
educated  people. 

We  all  know  that  the  savage  thinks  of  each  striking  phe- 
nomenon, or  group  of  phenomena,  as  caused  by  some  separate 
personal  agent ;  that  out  of  this  fetishistic  conception  there 
grows  up  a  polytheistic  conception,  in  which  these  minor  per- 
sonalities are  variously  generalized  into  deities  presiding  over 
different  divisions  of  nature ;  and  that  these  are  eventually 
furiher  generalized.  This  progressive  consolidation  of  causal 
agencies,  may  be  traced  in  the  creeds  of  all  races ;  and  is 
far  from  complete  in  the  creeds  of  the  most  advanced  races. 
The  unlettered  rustics  who  till  our  fields,  do  not  let  the  con- 
sciousness of  a  supreme  power  wholly  absorb  the  aboriginal 
conceptions  of  good  and  evil  spirits,  and  charms  or  secret 
potencies  dwelling  in  particular  objects.  The  earliest  mode 
of  thinking  changes,  only  as  fast  as  the  constant  relations 
among   phenomena   are    established.  Scarcely   less 


THE   SPECIAL-CREATION-HYPOTHESIS.  335 

familiar  is  tlie  truth,  that  while  accumulating  knowledge 
makes  these  conceptions  of  personal  causal  agents  gradually 
more  vague,  as  it  merges  them  into  general  causes,  it  also 
destroys  the  habit  of  thinking  of  them  as  working  after  the 
methods  of  personal  agents.  "We  do  not  now,  like  Kepler, 
assume  guiding  spirits  to  keep  the  planets  in  their  orbits. 
It  is  no  longer  the  universal  belief  that  the  sea  was  once  for 
all  mechanically  parted  from  the  dry  land;  or  that  the 
mountains  were  placed  where  we  see  them  by  a  sudden  cre- 
ative act.  All  but  a  narrow  class  have  ceased  to  suppose 
sunshine  and  storm  to  be  sent  in  some  arbitrary  succession. 
The  majority  of  educated  people  have  given  up  thinking  of 
epidemics  as  punishments  inflicted  by  an  angry  deity.  Nor 
do  even  the  common  people  regard  a  madman  as  one  pos- 
sessed by  a  demon.  That  is  to  say,  we  everywhere  see 
fading  away  the  anthropomorphic  conception  of  the  Un- 
known Cause.  In  one  case  after  another,  is  abandoned  that 
interpretation  which  ascribes  phenomena  to  a  will  analogous 
to  the  human  will,  working  by  methods  analogous  to  human 
methods. 

If,  then,  of  this  once-numerous  family  of  beliefs,  the  im- 
mense majority  have  become  extinct,  we  may  not  unrea- 
sonably expect  that  the  few  remaining  members  of  the  family 
will  become  extinct.  One  of  these  is  the  belief  we  are  here 
considering — the  belief  that  each  species  of  organism  was 
specially  created.  Many  who  in  all  else  have  abandoned 
the  aboriginal  theory  of  things,  still  hold  this  remnant  of  the 
aboriginal  theory.  Ask  any  tolerably-informed  man  whether 
he  accepts  the  cosmogony  of  the  Indians,  or  the  Greeks,  or 
the  Hebrews,  and  he  will  regard  the  question  as  next  to  an 
insult.  Yet  one  element  common  to  these  cosmogonies  he 
very  likely  retains :  not  bearing  in  mind  its  origin.  For 
whence  did  he  get  the  doctrine  of  special  creations  ?  Catechise 
him,  and  he  is  forced  to  confess  that  it  was  put  into  his  mind 
in  childhood,  as  one  portion  of  a  story  which,  as  a  whole,  ho 
has  long  since  rejected.     Why  this  fragment  is  likely  to  bo 

4 


33tt 


THE    EVOLL'TJON    OF    LIFE. 


right  while  all  the  rest  is  wrong,  he  is  unable  to  say.  May 
we  not  then  expect,  that  the  relinquishment  of  all  other 
parts  of  this  story,  will  bye  and  bye  be  followed  by  the 
relinquishment  of  this  remaining  part  of  it  ? 

§  112.  The  belief  which  we  find  thus  questionable,  both 
a.s  being  a  primitive  belief  and  as  being  a  belief  belonging  to 
nn  almost-extinct  family,  is  a  belief  that  is  not  countenanced 
by  a  single  fact.  No  one  ever  saw  a  special  creation ;  no 
one  ever  found  proof  of  an  indirect  kind,  that  a  special 
creation  had  taken  place.  It  is  significant,  as  Dr  Hooker 
remarks,  that  naturalists  who  suppose  new  species  to  be 
miraculously  originated,  habitually  suppose  the  origination 
to  occur  in  seme  region  remote  from  human  observation. 
'Wherever  the  order  of  organic  nature  is  exposed  to  the  view  of 
zoologists  and  botanists,  it  expels  this  conception ;  and  the 
conception  sur  rives  only  in  connexion  with  imagined  places, 
where  the  order  of  organic  phenomena  is  unknown. 

Besides  being  absolutely  without  evidence  to  give  it  exter- 
nal support,  this  hypothesis  of  special  creations  cannot  sup- 
port itself  internally  —  cannot  be  framed  into  a  coherent 
thought.  It  is  one  of  those  illegitimate  symbolic  concep- 
tions, so  continually  mistaken  for  legitimate  symbolic  concep- 
tions (First  Principles,  §  9),  because  they  remain  untested. 
Immediately  an  attempt  is  made  to  elaborate  the  idea  into 
anything  like  a  definite  shape,  it  proves  to  be  a  pseud-idea, 
admitting  of  no  definite  shape.  Is  it  supposed  that  a  new 
organism,  when  specially  created,  is  created  out  of  nothing  ? 
If  so,  there  is  a  supposed  creation  of  matter ;  and  the  crea- 
tion of  matter  is  inconceivable — implies  the  establishment  of 
a  relation  in  thought  between  nothing  and  something — a 
relation  of  which  one  term  is  absent — an  impossible  rela- 
tion. Is  it  supposed  that  the  matter  of  which  the  new  or- 
ganism consists,  is  not  created  for  the  occasion,  but  is  taken 
out  of  its  pre-existing  forms  and  arranged  into  a  new  form?  If 
so,  we  are  met  by  the  question — how  is  the  re-arrangement 


THE    SPECIAL -CREATION- HYPOTHESIS.  837 

effected  ?  Of  the  myriad  atoms  going  to  the  composition  of 
the  new  organism,  all  of  them  previously  dispersed  through 
the  neighbouring  air  and  earth,  does  each,  suddenly  dis- 
engaging itself  from  its  combinations,  rush  to  meet  the  rest, 
unite  with  them  into  the  appropriate  chemical  compounds, 
and  then  fall  with  certain  others  into  its  appointed  place  in 
the  aggregate  of  complex  tissues  and  organs  ?  Surely  thus 
to  assume  a  myriad  supernatural  impulses,  differing  in  their 
directions  and  amounts,  given  to  as  many  different  atoms,  is  a 
multiplication  of  mysteries  rather  than  the  solution  of  a 
mystery.  For  every  one  of  these  impulses,  not  being  the 
result  of  a  force  locally  existing  in  some  other  form,  implies 
the  creation  of  force ;  and  the  creation  of  force  is  just  as 
inconceivable  as  the  creation  of  matter.  And  thus  is  it  with 
all  attempted  ways  of  representing  the  process.  The  old 
Hebrew  idea  that  God  takes  clay  and  moulds  a  new  creature, 
as  a  potter  might  mould  a  vessel,  is  probably  too  grossly  an- 
thropomorphic to  be  accepted  by  any  modern  defender  of  the 
special-creation  doctrine.  But  having  abandoned  this  crude 
belief,  what  belief  is  he  prepared  to  substitute  ?  If  a  new 
organism  is  not  thus  produced,  then  in  what  way  is  a  new 
organism  produced  ?  or  rather — in  what  way  can  a  new 
organism  be  conceived  to  be  produced  ?  We  will  not  ask  for 
the  ascertained  mode,  but  will  be  content  with  a  mode 
that  can  be  consistently  imagined.  No  such  mode,  however, 
is  assignable.  Those  who  entertain  the  proposition  that  each 
kind  of  organism  results  from  a  divine  interposition,  do  so 
because  they  refrain  from  translating  words  into  thoughts. 
The  case  is  one  of  those  where  men  do  not  really  believe,  but 
rather  believe  they  believe.  For  belief,  properly  so  called, 
implies  a  mental  representation  of  the  thing  believed;  and 
no  such  mental  representation  is  here  possible. 

§  113.  If  we  imagine  mankind  to  be  contemplated  by 
some  creature  as  short-lived  as  an  ephemeron,  but  possessing 
intelligence  like  our  own — if  we  imagine  such  a  being  study- 


&38  THE   EVOLUTION   OF   LIF£. 

Lag  men  and  women,  'during  his  few  hours  of  life,  ana 
speculating  as  to  the  mode  in  which  they  came  into  existence  ; 
it  is  manifest  that,  reasoning  in  the  usual  way,  he  would 
euppose  each  man  and  woman  to  have  been  separately 
created.  ISTo  appreciable  changes  of  structure  occurring  in 
any  of  them  during  the  few  hours  over  which  hi&  observa- 
tions extended,  this  being  would  probably  infer  that  no 
changes  of  structure  were  taking  place,  or  had  taken  place  j 
and  that  from  the  outset,  each  man  and  woman  had  pos- 
sessed all  the  characters  then  visible — had  been  orginally 
formed  with  them.  This  would  naturally  be  the  first  im- 
pression. The  application  is  obvious.  A  human  life 
is  ephemeral  compared  with  the  life  of  a  species ;  and  even 
the  period  over  which  the  records  of  human  experience 
extend,  is  ephemeral  compared  with  the  life  of  a  species. 
There  is  thus  a  parallel  contrast  between  the  immensely-long 
series  of  changes  that  have  occurred  during  the  life  of  a 
species,  and  that  small  portion  of  the  series  open  to  our  view. 
And  there  is  no  reason  to  suppose  that  the  first  conclusion 
drawn  by  mankind  from  this  small  part  of  the  series  visible 
to  them,  is  any  nearer  the  truth,  than  would  be  the  conclu- 
sion of  the  supposed  ephemeral  being  respecting  men  and 
women. 

This  analogy,  suggesting  as  it  does  how  the  hypothesis  of 
special  creations  is  merely  a  formula  for  our  ignorance,  raises 
the  question — what  reason  have  we  to  assume  special  crea- 
tions of  species  but  not  of  individuals;  unless  it  be  that  in 
the  case  of  individuals  we  directly  know  the  process  to  be 
otherwise,  but  in  the  case  of  species  do  not  directly  know  it 
to  be  otherwise  ?  Have  we  any  ground  for  concluding  that 
species  were  specially  created,  except  the  ground  that  we 
have  no  immediate  knowledge  of  their  origin  ?  And  does  our 
ignorance  of  the  manner  in  which  they  arose,  warrant  us  in 
asserting  that  they  arose  by  special  creation  ? 

Another  question  is  suggested  by  this  analogy.  Those 
who,  in  the  absence  of  immediate  evidence  of  the  way  in 


THE   SPECIAL-CREATIGN-HYTOTHESIS.  339 

which  species  arose,  assert  that  tliey  arose  not  in  any  way 
analogous  to  that  in  which  individuals  arise,  but  in  a  totally 
distinct  way,  think  that  by  this  supposition  they  honour  the 
Unknown  Cause  of  things ;  and  they  oppose  any  antagonist 
doctrine  as  amounting  to  an  exclusion  of  divine  power  from 
the  world.  But  if  divine  power  is  demonstrated  by  the 
separate  creation  of  each  species,  would  it  not  have  been  still 
better  demonstrated  by  the  separate  creation  of  each  indivi- 
dual ?  "Why  should  there  exist  this  process  of  natural  gene- 
sis ?  THiy  should  not  omnipotence  have  been  proved  by  the 
supernatural  production  of  plants  and  animals  everywhere 
throughout  the  world  from  hour  to  hour  ?  Is  it  replied  that 
the  Creator  was  able  to  make  individuals  arise  from  one 
another  in  a  natural  succession,  but  not  to  make  species  thus 
arise  ?  This  is  to  assign  a  limit  to  power  instead  of  magni- 
fying it.  Is  it  replied  that  the  occasional  miraculous  origina- 
tion of  a  species  was  practicable,  but  that  the  perpetual  miracu- 
lous origination  of  countless  individuals  was  impracticable  ? 
This  also  is  a  derogation.  Either  it  was  possible  or  not  pos- 
sible to  create  species  and  individuals  after  the  same  general 
method.  To  say  that  it  was  not  possible  is  suicidal  in  those 
who  use  this  argument ;  and  if  it  was  possible,  it  is  required 
to  say  what  end  is  served  by  the  special  creation  of  species 
that  would  not  have  been  better  served  by  the  special  creation 
of  individuals.  Again,  what  is  to  be  thought  of  the 

fact  that  the  great  majority  of  these  supposed  special  creations 
took  place  before  mankind  existed  ?  Those  who  think  that  di- 
vine power  is  demonstrated  by  special  creations,  have  to  answer 
the  question — to  whom  demonstrated?  Tacitly  or  avowedly, 
they  regard  the  demonstrations  as  being  for  the  benefit  of 
mankind.  But  if  so,  to  what  purpose  were  the  millions 
of  these  demonstrations  which  took  place  on  the  Earth  when 
there  were  no  intelligent  beings  to  contemplate  them  ?  Did 
the  Unknowable  thus  demonstrate  his  power  to  himself? 
Few  will  have  the  hardihood  to  say  that  any  such  demon- 
stration was  needful.    There  is  no  choice  but  to  regard  them, 


340  THE    EVOLUTION    OF    LIFE. 

either  as  superfluous  exercises  of  power,  which  is  a  derogatory 
supposition,  or  as  exercises  of  power  that  were  necessary 
because  species  could  not  be  otherwise  produced,  which  is 
also  a  derogatory  supposition. 

§  114.  Those  who  espouse  the  hypothesis  of  special  cre- 
ations, entangle  themselves  in  other  theological  difficulties. 
This  assumption  that  each  kind  of  organism  was  specially 
designed,  carries  with  it  the  implication  that  the  designer 
intended  everything  that  results  from  the  design.  There  is 
no  escape  from  the  admission,  that  if  organisms  were  severally 
constructed  with  a  view  to  their  respective  ends ;  then 
the  character  of  the  constructor  is  indicated  both  by  the 
ends  themselves,  and  the  perfection  or  imperfection  with 
which  the  organisms  are  fitted  to  them.  Observe  the  con- 
sequences. 

Without  dwelling  on  the  question  put  in  a  recent  chap- 
ter, why  during  untold  millions  of  years  there  existed  on 
the  Earth  no  beings  endowed  with  capacities  for  wide 
thought  and  high  feeling,  we  may  content  ourselves  with 
asking  why,  at  present,  the  Earth  is  largely  peopled  by 
creatures  which  inflict  on  each  other,  and  on  themselves,  so 
much  suffering?  Omitting  the  human  race,  whose  defects 
and  miseries  the  current  theology  professes  to  account  for, 
and  limiting  ourselves  to  the  lower  creation,  what  must  we 
think  of  the  countless  different  pain-inflicting  appliances 
and  instincts  with  which  animals  are  endowed  ?  Not  only 
now,  and  not  only  ever  since  men  have  lived,  has  the  Earth 
been  a  scene  of  warfare  among  all  sentient  creatures ;  but 
palceontology  shows  us  that,  from  the  earliest  eras  geologi- 
cally recorded,  there  has  been  going  on  this  universal  carn- 
age. Fossil  structures,  in  common  with  the  structures  of 
existing  animals,  show  us  elaborate  weapons  for  destroying 
other  animals.  We  have  unmistakable  proof  that  through- 
out all  past  time,  there  has  been  a  perpetual  preying  of  the 
superior  on  the  inferior — a  ceaseless  devouring  of  the  weak 


THE  SPEOIAL-CREATION-HYPOTHESIS.  341 

by  the  strong.  ITow  is  this  to  be  explained  ?  How  happens 
it  that  animals  were  so  designed  as  to  render  this  bloodshed 
necessary  ?  How  happens  it  that  in  almost  every  species,  the 
number  of  individuals  annually  born  is  such  that  the  ma- 
jority die  of  starvation  or  by  violence  before  arriving  at  ma- 
turity? Whoever  contends  that  each  kind  of  animal  was 
specially  designed,  must  assert  either  that  there  was  a  deli- 
berate intention  on  the  part  of  the  Creator  to  produce  those 
results,  or  that  there  was  an  inability  to  prevent  them. 
Which  alternative  does  he  prefer  ?  To  cast  an  imputation  on 
the  divine  character,  or  assert  a  limitation  of  the  divine 
power  ?  It  is  useless  for  him  to  plead  that  the  destruction  of 
the  less  powerful  by  the  more  powerful,  is  a  means  of  pre- 
venting the  miseries  of  decrepitude  and  incapacity,  and 
therefore  works  beneficently.  For  even  were  the  chief  mor- 
tality among  the  aged  instead  of  among  the  young,  there 
would  still  arise  the  unanswerable  question — why  were  not 
animals  constructed  in  such  ways  as  to  avoid  these  evils  ? 
why  were  not  their  rates  of  multiplication,  their  degrees  of 
intelligence,  and  their  propensities,  so  adjusted  that  these 
sufferings  might  be  escaped  ?  And  if  decline  of  vigour  was 
a  necessary  accompaniment  of  age,  why  was  it  not  provided 
that  the  organic  actions  should  end  in  sudden  death,  when- 
ever they  fell  below  the  level  required  for  pleasurable  exist- 
ence ?  Will  any  one  who  contends  that  organisms  were 
specially  designed,  assert  that  they  could  not  have  been 
designed  so  as  to  prevent  suffering  ?  And  if  he  admits  that 
they  could  have  been  made  so  as  to  prevent  suffering,  will 
he  assert  that  the  Creator  preferred  so  making  them  as  to 
inflict  suffering  ? 

Even  as  thus  presented,  the  difficulty  is  sufficiently  great ; 
but  it  appears  immensely  greater  when  we  examine  the  facta 
more  closely.  So  long  as  we  contemplate  only  the  preying 
of  the  superior  on  the  inferior,  some  good  appears  to  be 
extracted  from  the  evil — a  certain  amount  of  life  of  a  higher 
order,  is  supported  by  sacrificing  a  great  deal  of  life  of  a 


342  THE    EVOLUTION    OF    LIFE. 

lower  order.  So  long,  too,  as  we  leave  out  all  mortality  but 
that  which,  by  carrying  off  the  least  perfect  members  of  each 
species,  leaves  the  most  perfect  members  to  continue  the 
species ;  we  see  some  compensating  benefit  reached  through 
the  suffering  inflicted.  But  what  shall  we  say  on  finding 
innumerable  cases  in  which  the  suffering  inflicted  brings  no 
compensating  benefit  ?  What  shall  we  say  when  we  see  the 
inferior  destroying  the  superior  ?  "What  shall  we  say  on 
discovering  elaborate  appliances  for  securing  the  prosperity 
of  organisms  incapable  of  feeling,  at  the  expense  of  misery 
to  organisms  capable  of  happiness  ? 

Of  the  animal  kingdom  as  a  whole,  more  than  half  the 
species  are  parasites.  "  The  number  of  these  parasites," 
says  Prof.  Owen,  "  may  be  conceived  when  it  is  stated  that 
almost  every  known  animal  has  its  peculiar  species,  and 
generally  more  than  one,  sometimes  as  many  as,  or  even 
more  kinds  than,  infest  the  human  body."  Passing  over  the 
evils  thus  inflicted  on  animals  of  inferior  dignity,  let  us  limit 
ourselves  to  the  case  of  man.  The  Bothriocephalus  latin 
and  the  Taenia  solium,  are  two  kinds  of  tape-worm,  which 
flourish  in  the  human  intestines ;  producing  great  constitu- 
tional disturbances,  sometimes  ending  in  insanity ;  and  from 
the  germs  of  the  Taenia,  when  carried  into  other  parts  of  the 
body,  arise  certain  partially-developed  forms  known  as  Cysti- 
cerci,  Echinococci,  and  Ccenuri,  which  cause  disorganization 
more  or  less  extensive  in  the  brain,  the  lungs,  the  liver, 
the  heart,  the  eye,  &c,  often  ending  fatally  after  long- 
continued  suffering.  Five  other  parasites,  belonging  to 
a  different  class,  are  found  in  the  viscera  of  man  —  the 
Trichocephahts,  the  Oxyuris,  the  Strongylus  (two  species), 
the  Ancylostomum,  and  the  Ascaris ;  which,  beyond  that 
defect  of  nutrition  which  they  necessarily  cause,  sometimes 
induce  certain  irritations  that  lead  to  complete  demoraliza- 
tion. Of  another  class  of  entozoa,  belonging  to  the  sub- 
division Trematoda,  there  are  five  kinds  found  in  different 
organs  of  the  human  body — the  liver  and    gall  ducts,   the 


THE   SPECIAL-CREATION-HYPOTHESIS.  343 

portal  vein,  the  intestine,  the  bladder,  the  eye.  Then  we 
have  the  Trichina  spiralis,  which  passes  through  one  phase  of 
its  existence  imbedded  in  the  muscles  and  through  another- 
phase  of  its  existence  in  the  intestine  ;  and  which,  by  the 
induced  disease  Trichiniasis,  has  lately  committed  such  ra- 
vages in  Germany,  as  to  cause  a  panic.  And  to  these  we 
must  add  the  Guinea-worm,  which  in  some  part  of  Africa 
and  India,  makes  men  miserable  by  burrowing  in  their  legs. 
From  this  list  of  entozoa,  which  is  by  no  means  complete, 
let  us  pass  to  the  epizoa.  There  are  two  kinds  of  Acari, 
one  of  them  inhabiting  the  follicles  of  the  skin,  and  the 
other  producing  the  itch.  There  are  other  creatures  that 
bury  themselves  beneath  the  skin,  and  lay  their  eggs  there  ; 
and  there  are  three  species  of  lice  which  infest  the  surface  of 
the  body.  Nor  is  this  all :  besides  animal  parasites,  there 
are  sundry  vegetal  parasites,  which  grow  and  multiply  at 
our  cost.  The  Sarcina  ventriculi  inhabits  the  stomach,  and 
produces  gastric  disturbance.  The  Leptothrix  buccalis  is 
extremely  general  in  the  mouth,  and  may  have  something 
to  do  with  the  decay  of  teeth.  And  besides  these,  there  are 
microscopic  fungi  which  produce  ringworm,  porrigo,  pityri- 
asis, thrush,  &c.  Thus  the  human  body  is  the 
habitat  of  parasites,  internal  and  external,  animal  and  ve- 
getal, numbering,  if  all  were  set  down,  some  two  or  three 
dozen  species ;  sundry  of  which  are  peculiar  to  man,  and 
many  of  which  produce  in  man  great  suffering  and  not  un- 
frequently  death.  What  interpretation  is  to  be  put  on  these 
facts  by  those  who  espouse  the  hypothesis  of  special  crea- 
tions ?  According  to  this  hypothesis,  all  these  parasites 
were  designed  with  a  view  to  their  respective  modes  of  life. 
They  were  endowed  with  constitutions  fitting  them  to  live 
by  absorbing  the  j  iices  of  the  human  body ;  they  were  fur- 
nished with  appliances,  often  of  a  formidable  kind,  enabling 
them  to  root  themselves  in  and  upon  the  human  body ;  and 
they  were  made  prolific  in  an  almost  incredible  degree,  that 
their  germs  might  have  a  sufficient  number  of  chances  of 


344  THE    EVOLUTION    OF    LIFE. 

finding  their  way  into  the  human  body.  In  short,  elaborate 
contrivances  were  combined  to  insure  the  continuance  of 
their  respective  races ;  and  to  make  it  impossible  for  the  suc- 
cessive generations  of  men  to  avoid  being  preyed  upon  by 
them.  "What  shall  we  say  to  this  arrangement  ?  Shall  we 
say  that  man,  "  the  head  and  crown  of  things,"  was  provided 
as  a  habitat  for  these  parasites  ?  Or  shall  we  say  that  these 
degraded  creatures,  incapable  of  thought  or  enjoyment,  were 
created  that  they  might  cause  unhappiness  to  man?  One 
or  other  of  these  alternatives  must  be  chosen  by  those  who 
contend  that  every  kind  of  organism  was  separately  devised 
by  the  Creator.  "Which  do  they  prefer  ?  With  the  concep- 
tion of  two  antagonistic  powers,  which  severally  work  good 
and  evil  in  the  world,  the  facts  are  congruous  enough.  But 
with  the  conception  of  a  supreme  beneficence,  this  gratuitous 
infliction  of  misery  on  man,  in  common  with  all  other  terres 
trial  creatures  capable  of  feeling,  is  absolutely  incompatible. 

5  115.  See  then  the  results  of  our  examination.  The 
belief  in  special  creations  of  organisms,  is  a  belief  that  arose 
among  men  during  the  era  of  profoundest  darkness  ;  and  it 
belongs  to  a  family  of  beliefs  which  have  nearly  all  died  out 
as  enlightenment  has  increased.  It  is  without  a  solitary 
established  fact  on  which  to  stand ;  and  when  the  attempt  is 
made  to  put  it  into  definite  shape  in  the  mind,  it  turns  out  to 
be  only  a  pseud-idea.  This  mere  verbal  hypothesis,  which 
men  idly  accept  as  a  real  or  thinkable  hypothesis,  is  of  the 
same  nature  as  would  be  one,  based  on  a  day's  observation  of 
human  life,  that  each  man  and  woman  was  specially  created 
— an  hypothesis  not  suggested  by  evidence,  but  by  lack  of 
.evidence — an  hypothesis  which  formulates  absolute  ignorance 
into  a  semblance  of  positive  knowledge.  Further,  we  see  that 
this  hypothesis,  wholly  without  support,  essentially  inconceiv- 
able, and  thus  failing  to  satisfy  men's  intellectual  need  of  an 
interpretation,  fails  also  to  satisfy  their  moral  sentiment. 
It  is  quite  inconsistent  with  those  conceptions  of  the  divina 


THE    SPECIAL-CREATION-HYPOTHESIS.  345 

nature  which,  they  profess  to  entertain.  If  infinite  power 
was  to  be  demonstrated,  then,  either  by  the  special  creation 
of  every  individual,  or  by  the  production  of  species  after  a 
method  akin  to  that  in  which  individuals  are  produced,  it 
would  be  better  demonstrated  than  by  the  use  of  the  two 
methods  which  the  hypothesis  assumes  to  be  necessary.  And 
if  infinite  goodness  was  to  be  demonstrated,  then,  not  only 
do  the  provisions  of  organic  structure,  if  they  are  especially 
devised,  fail  to  demonstrate  it ;  but  there  is  an  enormous 
mass  of  them  which  imply  malevolence  rather  than  bene- 
volence. 

Thus,  however  regarded,  the  hypothesis  of  special  creations 
turns  out  to  be  worthless  —  worthless  by  its  derivation ; 
worthless  in  its  intrinsic  incoherence  ;  worthless  as  absolutely 
without  evidence ;  worthless  as  not  supplying  an  intellectual 
need  ;  worthless  as  not  satisfying  a  moral  want.  We  must 
therefore  consider  it  as  counting  for  nothing,  in  opposition 
to  any  other  hypothesis  respecting  the  origin  of  organic 
being?. 


23 


CHAPTER  III. 

GENERAL    ASPECTS    OF    THE    EVOLUTIOX-HYPOTnESIS. 

§  116.  Just  as  the  supposition  that  races  of  organisms 
have  been  specially  created,  is  discredited  by  its  origin ;  so, 
conversely,  the  supposition  that  races  of  organisms  have 
been  evolved,  is  credited  by  its  origin.  Instead  of  being 
a  conception  suggested  and  accepted  when  mankind  were 
profoundly  ignorant,  it  is  a  conception  born  in  times  of  com- 
parative enlightenment.  Moreover,  the  belief  that  all  organic 
forms  have  arisen  in  conformity  with  uniform  laws,  instead 
of  through  breaches  of  uniform  laws,  is  a  belief  that  has 
come  into  existence  in  the  most-instructed  class,  living  in 
these  better-instructed  times.  Not  among  those  who  have 
paid  no  attention  to  the  order  of  Nature,  has  this  idea  made 
its  appearance ;  but  among  those  whose  pursuits  have  famil- 
iarized them  with  the  order  of  Nature.  Thus  the  derivation 
of  this  modern  hypothesis  is  as  favourable  as  that  of  the 
aucient  hypothesis  is  unfavourable 

§  117.  A  kindred  antithesis  exists  between  the  two  fami- 
lies of  beliefs,  to  which  the  beh'efs  we  are  comparing  severally 
belong.  While  the  one  family  has  been  dying  out,  the 
other  family  has  been  multiplying.  Just  as  fast  as  men 
have  ceased  to  regard  different  classes  of  phenomena  as 
caused  by  special  personal  agents,  acting  irregularly ;  so  fast 
have  they  come  to  regard  these  different  classes  of  phe- 
nomena as  caused  by  a  general  agency  acting  uniformly — the 


THE  EVOLUTION-HYPOTHESIS.  347 

two  changes  being  correlative.  And  as,  on  the  one  hand, 
the  hypothesis  that  each  species  resulted  from  a  supernatural 
act,  having  lost  nearly  all  its  kindred  hypotheses,  may  be 
t  xpected  soon  to  become  extinct ;  so,  on  the  other  hand,  the 
1  ypothesis  that  each  species  resulted  from  the  action  of  na- 
t  ural  causes,  being  one  of  an  ever-increasing  family  of  hypo- 
theses, may  be  expected  to  survive  and  become  established. 

Still  greater  will  the  probability  of  its  survival  and  estab- 
lishment appear,  when  we  observe  that  it  is  one  of  a  particu- 
lar genus  of  hypotheses  that  has  been  rapidly  extending. 
The  interpretation  of  phenomena  as  resulting  from  Evolution, 
has  been  independently  showing  itself  in  various  fields  of 
inquiry,  quite  remote  from  one  another.  The  supposition 
that  the  Solar  System  has  been  gradually  evolved  out  of  dif- 
fused matter,  is  a  supposition  wholly  astronomical  in  its 
origin  and  application.  Geologists,  without  being  led  thereto 
by  astronomical  considerations,  have  been  step  by  step  ad- 
vancing towards  the  conviction,  that  the  Earth  has  reached 
its  present  varied  structure  through  a  process  of  Evolution. 
The  inquiries  of  biologists  have  proved  the  falsity  of  the  once 
general  belief,  that  the  germ  of  each  organism  is  a  minute 
repetition  of  the  mature  organism,  differing  from  it  only  in 
bulk ;  and  they  have  shown,  contrariwise,  that  every  organ- 
ism, arising  out  of  apparently-uniform  matter,  advances  to  its 
ultimate  multiformity  through  insensible  changes.  Among 
philosophical  politicians,  there  has  been  spreading  the  per- 
ception that  the  progress  of  society  is  an  evolution :  the 
truth  that  "  constitutions  are  not  made  but  grow,"  is  a  part 
of  the  more  general  truth  that  societies  are  not  made  but 
»row.  It  is  now  universally  admitted  by  philologists,  that 
languages,  instead  of  being  artificially  or  supernaturally 
formed,  have  been  developed.  And  the  histories  of  religion, 
of  philosophy,  of  science,  of  the  fine  arts,  and  of  the  indus- 
trial arts,  show  that  these  have  passed  through  stages  as  un- 
obtrusive as  those  through  which  the  mind  of  a  child  passes 
on  its  way  to  maturity.     If   then,  the  recognition  of  evolu- 


348  THE    EVOLUTION    OF    LIFE. 

tion  as  the  law  of  many  diverse  orders  of  phenomena,  Laa 
been  spreading ;  may  we  not  say  that  there  thence  arises  the 
probability  that  evolution  will  presently  be  recognized  as  the 
law  of  the  phenomena  we  are  considering  ?  Each  further  ad- 
vance of  knowledge,  confirms  the  belief  in  the  unity  of 
Nature  ;  and  the  discovery  that  evolution  has  gone  on,  or  is 
going  on,  in  so  many  departments  of  Nature,  becomes  a  rea- 
son for  believing  that  there  is  no  department  of  Nature  in 
which  ii  does  not  go  on. 

§  118.  The  Irypotheses  of  Special  Creation  and  Evolution, 
are  no  less  contrasted  in  respect  of  their  legitimacy  as  hy- 
potheses. While,  as  we  have  seen,  the  one  belongs  to  that 
order  of  symbolic  conceptions  which  are  proved  to  be  illusive 
by  the  impossibility  of  realizing  them  in  thought ;  the  other 
is  one  of  those  symbolic  conceptions  which  are  more  or  less 
completely  realizable  in  thought.  The  production  of  all 
organic  forms  by  the  slow  accumulation  of  modifications  upon 
modifications,  and  by  the  slow  divergences  resulting  from 
the  continual  addition  of  differences  to  differences,  is  mentally 
representable  in  outline,  if  not  in  detail.  Various  orders  of 
our  experiences  enable  us  to  conceive  the  process.  Let  us 
look  at  one  of  the  simplest. 

There  is  no  apparent  similarity  between  a  straight  line 
and  a  circle.  The  one  is  a  curve  ;  the  other  is  defined  as 
without  curvature.  The  one  encloses  a  space ;  the  other 
will  not  enclose  a  space  though  produced  for  ever.  The  one 
is  finite ;  the  other  may  be  infinite.  Yet,  opposite  as  the 
two  are  in  all  their  properties,  they  may  be  connected  together 
by  a  series  of  lines  no  one  of  which  differs  from  the  adjacent 
ones  in  any  appreciable  degree.  Thus,  if  a  cone  be  cut  by 
a  plane  at  right  angles  to  its  axis,  we  get  a  circle.  If,  instead 
of  being  perfectly  at  right  angles,  the  plane  subtends  with 
the  axis  an  angle  of  89°  59',  we  have  an  ellipse  which  no 
human  eye,  even  when  aided  by  an  accurate  pair  of  compasses, 
can  distinguish  from  a  circle.    Decreasing  the  angle  minute 


THE   EVOLUTION-HYPOTHESIS.  349 

by  mimite,  the  ellipse  becomes  first  perceptibly  eccentric,  then 
manifestly  so,  and  by  and  by  acquires  so  immensely  elongated 
a  form,  as  to  bear  no  recognizable  resemblance  to  a  circle. 
By  continuing  this  process,  the  ellipse  changes  insensibly  into 
a  parabola.  On  still  further  diminishing  the  angle,  the  para- 
bola becomes  an  hyperbola.  And  finally,  if  the  cone  be 
made  gradually  more  obtuse,  the  hyperbola  passes  into  a 
straight  line,  as  the  angle,  of  the  cone  approaches  180°.  Now 
here  we  have  five  different  species  of  line — circle,  ellipse, 
parabola,  hyperbola,  and  straight  line — each  having  its  pecu- 
liar properties  and  its  separate  equation,  and  the  first  and 
last  of  which  are  quite  opposite  in  nature,  connected  together 
as  members  of  one  series,  all  producible  by  a  single  process 
of  insensible  modification. 

But  the  experiences  which  most  clearly  illustrate  to  us 
the  process  of  general  evolution,  are  our  experiences  of 
special  evolution,  repeated  in  every  plant  and  animal.  Each 
organism  exhibits,  within  a  short  space  of  time,  a  series 
of  changes  which,  when  supposed  to  occupy  a  period  inde- 
finitely great,  and  to  go  on  in  various  ways  instead  of  one 
way,  give  us  a  tolerably  clear  conception  of  organic  evo- 
lution in  general.  In  an  individual  development,  we  have 
compressed  into  a  comparatively  infinitesimal  sj)ace,  a  series 
of  metamorphoses  equally  vast  with  those  which  the  hypo- 
thesis of  evolution  assumes  to  have  taken  place  during  those 
immeasurable  epochs  that  the  Earth's  crust  tells  us  of.  A 
tree  differs  from  a  seed  immeasurably  in  every  respect — 
in  bulk,  in  structure,  in  colour,  in  form,  in  specific  gravity, 
in  chemical  composition  :  differs  so  greatly  that  no  visible 
resemblance  of  any  kind  can  be  pointed  out  between  them 
Yet  is  the  one  changed  in  the  course  of  a  few  years  into  tho 
other  :  changed  so  gradually,  that  at  no  moment  can  it  be 
eaid — Now  the  seed  ceases  to  be,  and  the  tree  exists.  What 
can  be  more  widely  contrasted  than  a  newly-born  child  and 
the  small,  semi-transparent,  gelatinous  spherule  constituting 
the  human  ovum  ?    The  infant  is  so  complex  in  structure 


350  THE    EVOLUTION    OF   LIFE. 

that  a  cyclopedia  is  needed  to  describe  its  constituent  parts* 
The  germinal  vesicle  is  so  simple  that  it  may  be  defined  m 
a  line.  Nevertheless,  a  few  months  suffice  to  develope  the 
one  out  of  the  other ;  and  that,  too,  by  a  series  of  modifica- 
tions so  small,  that  were  the  embryo  examined  at  successive 
minutes,  even  a  microscope  would  with  difficulty  disclose 
any  sensible  changes.  Aided  by  such  facts,  the  conception 
of  general  evolution  may  be  rendered  as  definite  a  concep- 
tion as  any  of  our  complex  conceptions  can  be  rendered.  If 
instead  of  the  successive  minutes  of  a  child's  foetal  life,  we 
take  successive  generations  of  creatures — if  we  regard  the  suc- 
cessive generations  as  differing  from  each  other  no  more  than 
the  foetus  did  in  successive  minutes ;  our  imaginations  must 
indeed  be  feeble  if  we  fail  to  realize  in  thought,  the  evolu- 
tion of  the  most  complex  organism  out  of  the  simplest.  If  a 
single  cell,  under  appropriate  conditions,  becomes  a  man  in 
the  space  of  a  few  years ;  there  can  surely  be  no  difficulty  in 
understanding  how,  under  appropriate  conditions,  a  cell  may, 
in  the  course  of  untold  millions  of  years,  give  origin  to  the 
human  race. 

It  is  true  that  many  minds  are  so  unfurnished  with  those 
experiences  of  Nature  out  of  which  this  conception  is  built, 
that  they  find  difficulty  in  forming  it.  Habitually  looking 
at  things  rather  in  their  statical  than  in  their  dynamical 
aspects,  they  never  realize  the  fact  that,  by  small  increments 
of  modification,  any  amount  of  modification  may  in  time  be 
generated.  That  surprise  which  they  feel  on  finding  one 
whom  they  last  saw  as  a  boy,  grown  into  a  man,  becomes 
incredulity  when  the  degree  of  change  is  greater.  To  such, 
the  hypothesis  that  by  any  series  of  changes  a  protozoon 
stould  ever  give  origin  to  a  mammal,  seems  grotesque — as 
grotesque  as  did  Galileo's  assertion  of  the  Earth's  movement 
eeem  to  the  Aristotleans ;  or  as  grotesque  as  the  assertion  of 
the  Earth's  sphericity  seems  now  to  the  New  Zealanders. 
But  those  who  accept  a  literally-unthinkable  proposition  as 


THE   EVOLUTiON-lliTOTHESlS.  351 

quite  satisfactory,  may  not  unnaturally  be  expected  to  make  a 
converse  mistake. 

§  119.  The  hypothesis  of  evolution  is  contrasted  with 
the  hypothesis  of  special  creations,  in  a  further  respect-  It  is 
not  simply  legitimate  instead  of  illegitimate,  because  repre- 
suitable  in  thought  instead  of  unrepresentable ;  but  it  has 
the  support  of  some  evidence,  instead  of  being  absolutely 
unsupported  by  evidence.  Though  the  facts  at  present  as- 
signable in  direct  proof  that  by  progressive  modifications, 
races  of  organisms  that  are  apparently  distinct  may  result 
from  antecedent  races,  are  not  sufficient ;  yet  there  are  nu- 
merous facts  of  the  order  required.  It  has  been  shown 
beyond  all  question  that  unlikenesses  of  structure  gradually 
arise  among  descendants  from  the  same  stock.  We  find  that 
there  is  going  on  a  modifying  process  of  the  kind  alleged  as 
the  source  of  specific  differences :  a  process  which,  though 
slow  in  its  action,  does,  in  time,  if  the  circumstances  demand 
it,  produce  conspicuous  changes — a  process-  which,  to  all 
appearance,  would  produce  in  the  millions  of  years,  and  under 
the  great  varieties  of  conditions  which  geological  records 
imply,  any  amount  of  change. 

In  the  chapters  on  "Heredity"  and  "Variation,"  con- 
tained in  the  preceding  Part,  many  such  facts  were  given ; 
and  plenty  more  might  be  added.  Although  comparatively 
little  attention  has  been  paid  to  the  matter  until  recent  times, 
the  evidence  already  collected  shows  that  there  take  place  in 
successive  generations,  alterations  of  structure  quite  as 
marked  as  those  which,  in  successive  short  intervals,  arise  ir 
a  devekming  embryo — nay,  often  much  more  marked  ;  since, 
besides  differences  due  to  changes  in  the  relative  sizes  ol 
parts,  there  sometimes  arise  differences  due  to  additions  and 
suppressions  of  parts.  The  structural  modification  proved 
to  have  taken  place  since  organisms  have  been  observed,  is 
not  less  than  the  hypothesis  demands — bears  as  great  a  ratio 


352  THE    EVOLUTION    OF    LIFE. 

to  this  brief  period,  as  the  total  amount  of  structural  change 
seen  in  the  evolution  of  a  complex  organism  out  of  a  simple 
germ,  bears  to  that  vast  period  during  which  living  forms 
have  existed  on  the  Earth. 

We  have,  indeed,  much  the  same  kind  and  quantity  of 
direct  evidence  that  all  organic  beings  have  gradually  amen 
through  the  actions  of  natural  causes,  which  we  have  that  all 
the  structural  complexities  of  the  Earth's  crust  have  arisen 
through  the  actions  of  natural  causes.  It  may,  I  think,  be 
fairly  said,  that  between  the  known  modifications  undergone  by 
organisms,  and  the  totality  of  modifications  displayed  in  their 
structures,  there  is  no  greater  disproportion  than  between  the 
geological  changes  which  have  been  witnessed,  and  the  to- 
tality of  geological  changes  supposed  to  be  similarly  caused. 
Here  and  there  are  pointed  out  sedimentary  deposits  now 
slowly  taking  place.  At  this  place,  it  is  proved  that  a  shore 
has  been  encroached  on  by  the  sea  to  a  considerable  extent 
wi'iiin  recorded  times ;  and  at  another  place,  an  estuary  is 
known  to"  have  become  shallower  within  the  space  of  some 
generations.  In  one  region  a  general  upheaval  is  going  on 
at  the  rate  of  a  few  feet  in  a  century ;  wbi1^  *h  asather 
region  occasional  earthquakes  are  shown  to  cause  slight 
variations  of  level.  Appreciable  amounts  of  denudation  by 
water  are  visible  in  some  localities ;  and  in  other  localities 
glaciers  are  detected  in  the  act  of  grinding  down  the  rocky  sur- 
faces over  which  they  glide.  But  the  changes  thus  instanced, 
are  infinitesimal  compared  with  the  aggregate  of  changes  tc 
which  the  Earth's  crust  testifies,  even  in  its  still  extant  sys- 
tems of  strata.  If,  then,  from  the  small  changes  now  being 
wrought  on  the  Earth's  crust  by  natural  agencies,  we  may 
legitimately  conclude  that  by  such  natural  agencies  acting 
through  vast  epochs,  all  the  structural  complexities  of  the 
Earth's  crust  have  been  produced;  may  we  not  from  the 
small  known  modifications  produced  in  races  of  organisms 
by  natural  agencies,  similarly  infer  that  from  natural  ageu- 


THE    EVOLUTION-HYPOTHESIS.  353 

ciee  have  slowly  arisen  all  those  structural  complexities  which 
we  see  in  them.  ? 

The  hypothesis  of  Evolution  then,  has  direct  support  from 
facts  which,  though  small  in  amount,  are  of  the  kind  required; 
and  the  proportion  which  these  facts  bear  to  the  conclusion 
drawn,  seems  as  great  as  is  the  proportion  between  facts  and 
conclusion  which,  in  another  case,  produces  acceptance  of  the 
conclusion. 

§  120.  Let  us  put  ourselves  for  a  moment  in  the  position  of 
those  who,  from  their  experiences  of  human  modes  of  action, 
draw  inferences  respecting  the  mode  of  action  of  that  ultimate 
power  manifested  to  us  through  phenomena.  We  shall  find 
the  supposition  that  each  kind  of  organism  was  separately 
designed  and  put,  together,  to  be  much  less  consistent  with 
their  professed  conception  of  this  ultimate  power,  than  is  the 
supposition  that  all  kinds  of  organisms  have  resulted  from 
one  unbroken  process.  Irregularity  of  method  is  a  mark  of 
weakness.  Uniformity  of  method  is  a  mark  of  strength.  Con- 
tinual interposition  to  alter  a  pre-arranged  set  of  actions, 
implies  defective  arrangement  in  those  actions.  The  main- 
tenance of  those  actions,  and  the  working  out  by  them  of  the 
highest  residts,  implies  completeness  of  arrangement.  If 
human  workmen,  whose  machines  as  at  first  constructed 
require  perpetual  adjustment,  show  their  increasing  skill  by 
making  their  machines  self-adjusting  ;  then,  those  who  figure 
to  themselves  tlia  production  of  the  world  and  its  inhabitants 
by  a  "  Great  Artificer,"  must  admit  that  the  achievement  of 
this  end  by  a  persistent  process,  adapted  to  all  contingenci  *, 
implies  greater  skill  than  its  achievement  by  the  process  of 
meeting  the  contingencies  as  they  severally  arise. 

So,  too,  it  is  with  the  contrast  under  its  moral  aspect.  "We 
saw  that  to  the  hypothesis  of  special  creations,  a  difficulty 
is  presented  by  the  absence  of  high  forms  of  life  during  those 
immeasurable  epochs  of  the  Earth's  existence  which  geology 


354  THE    EVOLUTION    OF   LIFE. 

records.  But  to  the  hypothesis  of  evolution,  this  absence  ie 
no  such  obstacle.  Suppose  evolution,  and  this  question  is 
necessarily  excluded.  Suppose  special  creations,  and  this 
question,  unavoidably  raised,  can  have  no  satisfactory  an- 
swer. Still  more  marked  is  this  contrast  between  the 
two  hypotheses,  in  presence  of  that  vast  amount  of  suf- 
fering entailed  on  all  orders  of  sentient  beings,  by  their 
imperfect  adaptations  to  their  conditions  of  life ;  and  the 
further  vast  amount  of  suffering  entailed  on  them  by  enemies 
and  by  parasites.  We  saw  that  if  organisms  were  severally 
designed  for  their  respective  places  in  Nature,  the  inevitable 
conclusion  is,  that  these  thousands  of  kinds  of  inferior  organ- 
isms which  prey  upon  superior  organisms,  were  intended  to 
inflict  all  the  pain  and  mortality  which  results.  But  the  hy- 
pothesis of  evolution  involves  us  in  no  such  dilemma.  Slowly, 
bat  surely,  evolution  brings  about  an  increasing  amount 
of  happiness :  all  evils  being  but  incidental.  By  its  essen- 
tial nature,  the  process  must  everywhere  produce  greater 
fitness  to  the  conditions  of  existence ;  be  they  what  they  may. 
Applying  alike  to  the  lowest  and  the  highest  forms  of  organ- 
ization, there  is  in  all  cases  a  progressive  adaptation ;  and  a 
survival  of  the  most  adapted.  If,  in  the  uniform  working 
out  of  the  process,  there  are  evolved  organisms  of  low  types, 
which  prey  on  those  of  higher  types,  the  evils  inflicted  form 
but  a  deduction  from  the  average  benefits.  The  universal 
and  necessary  tendency  towards  supremacy  and  multiplica- 
tion of  the  best,  applying  to  the  organic  creation  as  a  whole 
as  well  as  to  each  species,  is  ever  diminishing  the  damage 
done — tends  ever  to  maintain  those  most  superior  organisms 
wh  ich,  in  one  way  or  other,  escape  the  invasions  of  the  infe- 
rior, and  so  tends  to  produce  a  type  less  liable  to  the  inva- 
sions of  the  inferior.  Thus  the  evils  accompanying  evolu- 
tion are  ever  being  self-eliminated.  Though  there  may  arise 
the  question  —  Why  could  they  not  have  been  avoided? 
there  does  not  arise  the  question — Why  were  they  deliber- 


THE  EVOLUTION- HYPOTHESIS.  355 

ately  inflicted?     Whatever  may  "be  thought  of  them,  it  is 
clear  that  they  do  not  imply  gratuitous  malevolence. 

§  121.  In  all  respects,  then,  the  hypothesis  of  evolution 
contrasts  favourably  with  the  hypothesis  of  special  creation. 
It  has  arisen  in  comparatively-instructed  times,  and  in  the 
most  cultivated  class.  It  is  one  of  those  beliefs  in  the  uni- 
form concurrence  of  phenomena,  which  are  gradually  sup- 
planting beliefs  in  their  irregular  and  arbitrary  concurrence ; 
and  it  belongs  to  a  genus  of  these  beliefs  which  has  of  late 
been  rapidly  spreading.  It  is  a  definitely- conceivable  hypo- 
thesis :  being  simply  an  extension  to  the  organic  world  at 
large,  of  a  conception  built  from  our  experiences  of  individual 
organisms  ;  just  as  the  hypothesis  of  universal  gravitation, 
was  an  extension  of  the  conception  which  our  experiences 
of  terrestrial  gravitation  had  produced.  This  definitely-con- 
ceivable hypothesis,  besides  the  support  of  numerous  ana- 
logies, has  the  support  of  direct  evidence  :  we  have  positive 
proof  that  there  is  going  on  a  process  of  the  kind  alleged ; 
and  though  the  results  of  this  process,  as  actually  witnessed, 
are  minute  in  comparison  with  the  totality  of  results  ascribed 
to  it,  yet  they  bear  to  such  totality,  a  ratio  as  great  as  that  by 
which  an  analogous  hj'-pothesis  is  justified.  Lastly,  that  senti- 
ment which  the  doctrine  of  special  creations  is  thought  neces- 
sary to  satisfy,  is  much  better  satisfied  by  the  doctrine  of  evolu- 
tion ;  since  this  doctrine  raises  no  contradictory  implications 
respecting  the  Unknown  Cause,  such  as  are  raised  by  the 
antagonist  doctrine. 

And  now,  having  observed  how,  imder  its  most  general 
aspects,  the  hypothesis  of  evolution  commends  itself  to  us, 
by  its  derivation,  by  its  coherence,  by  its  analogies,  by  its 
direct  evidence,  by  its  implications  ;  let  us  go  on  to  consider 
the  several  orders  of  facts  which  yield  indirect  support  to  it. 
We  will  begin  by  noting  the  harmonies  that  exist  between 
it,,  and  sundry  of  the  inductions  set  forth  in  Part  II, 


CHAPTER   IV. 

THE    ARGUMENTS    FROM    CLASSIFICATION. 

§  122.  In  §  103,  we  saw  that  the  relations  which  exist 
among  the  species,  genera,  orders,  and  classes  of  organisms, 
are  not  interpretable  as  results  of  any  such  causes  as  have 
been  usually  assigned.  We  will  here  consider  whether  they 
are  interpretable  as  the  results  of  evolution.  Let  us  first 
contemplate  some  familiar  facts. 

The  Norwegians,  Swedes,  Danes,  Germans,  Dutch,  and 
Anglo-Saxons,  form  together  a  group  of  Scandinavian  races, 
that  are  but  slightly  divergent  in  their  characters.  Welsh, 
Irish,  and  Highlanders,  though  they  have  differences,  have 
not  differences  such  as  to  hide  a  decided  community  of  na- 
ture :  they  are  classed  together  as  Celts.  Between  the 
Scandinavian  race  as  a  whole  and  the  Celtic  race  as  a 
whole,  there  is  a  recognized  distinction  greater  than  that 
between  the  sub-divisions  which  make  up  one  or  the  other. 
And  the  several  peoples  inhabiting  Southern  Europe  are  more 
nearly  allied  to  one  another,  than  the  aggregate  they  form  is 
allied  to  the  aggregates  of  Northern  peoples.  If,  again,  we 
compare  these  European  varieties  of  man  taken  as  a  group, 
with  that  group  of  Eastern  varieties  which  had  a  common 
origin  with  it,  we  see  a  stronger  contrast  than  between  the 
European  varieties  themselves.  And  once  more,  ethnolo- 
gists find  differences  of  still  higher  importance,  between  the 
Aryan  stock  as  a  whole  and  the  Mongolian  stock  as  a  whole, 


THE    ARGUMENTS    FROM    CLASSIFICATION.  857 

or  the  Negro  stock  as  a  whole.  Though  these  contrasts 
are  partially  obscured  by  intermixtures ;  yet  they  are  not  so 
obscured  as  to  hide  the  truths  that  the  inost-nearly-allied 
varieties  of  man,  are  those  which  diverged  from  one  ano- 
ther at  a  comparatively-recent  period ;  that  each  group 
of  nearly-allied  varieties,  is  more  strongly  contrasted  with 
other  such  groups  that  had  a  common  origin  with  it  at  a 
remoter  period ;  and  so  on,  imtil  we  come  to  the  largest 
groups,  which  are  the  most  strongly  contrasted,  and  of  whose 
divergence  no  trace  is  extant. 

The  relations  existing  among  the  classes  and  sub-classes 
of  languages,  have  been  briefly  referred  to  by  Mr  Darwin,  in 
illustration  of  his  argument.  We  know  that  languages  have 
arisen  by  evolution.  Let  us  then  see  what  grouping  of  them 
evolution  has  produced.  On  comparing  the  dialects  of  adja- 
cent counties  in  England,  we  find  that  their  differences  are  so 
small  as  scarcely  to  distinguish  them.  Between  the  dialects 
of  the  Northern  counties  taken  together,  and  those  of  the 
Southern  counties  taken  together,  the  contrast  is  stronger. 
These  clusters  of  dialects,  together  with  those  of  Scotland  and 
Ireland,  are  nevertheless  so  similar,  that  we  regard  them  as 
one  language.  The  several  languages  of  Scandinavian  Eu- 
rope, including  English,  are  much  more  unlike  one  ano- 
ther, than  are  the  several  dialects  which  each  of  them  in- 
cludes ;  in  correspondence  with  the  fact  that  they  diverged 
from  one  another  at  earlier  periods  than  did  their  respective 
dialects.  The  Scandinavian  languages  have  nevertheless  a 
certain  community  of  character,  which  distinguishes  them  as  a 
group  from  the  languages  of  Southern  Europe ;  between 
which  there  are  general  and  special  affinities  that  similarly 
unite  them  into  a  group  formed  of  sub-groups  containing  sub- 
sub-groups.  And  this  wider  divergence  between  the  order 
of  languages  spoken  in  Northern  Europe,  and  the  order  of 
languages  spoken  in  Southern  Europe,  answers  to  the  longer 
time  that  has  elapsed  since  their  differentiation  commenced 
Further,  these  two  orders  of  modern  European  languages,  as 


Ji58  THE    EVOLUTION    OF    L1FK. 

well  as  Latin  and  Greek  and  certain  extinct  and  spoken 
languages  of  the  East,  are  shown  to  have  traits  iu 
common,  which,  notwithstanding  the  wide  gaps  between 
them,  unite  them  together  as  one  great  class  of  Aryan  lan- 
guages; radically  distinguished  from  the  classes  of  lan- 
guages spoken  by  the  other  great  divisions  of  the  human 
race. 

§  123.  Now  this  kind  of  subordination  of  groups,  which 
we  see  arises  in  the  course  of  continuous  descent,  multiplica- 
tion, and  divergence,  is  just  the  kind  of  subordination  of 
groups  which  plants  and  animals  exhibit :  it  is  just  this 
kind  of  subordination  which  has  thrust  itself  on  the  attention 
of  naturalists,  in  spite  of  pre-conceptions. 

The  original  idea  was  that  of  arrangement  in  linear  order. 
We  saw  that  even  after  a  considerable  acquaintance  with  the 
structures  of  organisms  had  been  acquired,  naturalists  con- 
tinued their  efforts  to  reconcile  the  facts  with  the  notion  of  a 
uni-serial  succession.  The  accumulation  of  evidence  necessi- 
tated the  breaking  up  of  the  imagined  chain  into  groups 
and  sub-groups.  Gradually  there  arose  the  conviction  that 
these  groups  do  not  admit  of  being  placed  in  a  line.  And  the 
conception  finally  arrived  at,  is,  that  of  certain  great  sub- 
kingdoms,  very  widely  divergent,  each  made  up  of  classes 
much  less  widely  divergent,  severally  containing  orders  still 
less  divergent;  and  so  on  with  genera  and  species.  The 
diagram  on  page  303,  shows  the  general  relations  of  these 
d  i  visions  in  their  degrees  of  subordination. 

Hence  this  "  grand  fact  in  natural  history  of  the  subordina- 
tion of  group  under  group,  which  from  its  familiarity  does 
not  always  sufficiently  strike  us,"  is  perfectly  in  harmony 
with  the  hypothesis  of  evolution.  The  extreme  significance 
of  this  kind  of  relation  among  organic  forms,  is  dwelt  on  by 
Mr  Dai  win  ;  who  shows  how  an  ordinary  genealogical  tree 
represents,  on  a  small  scale,  a  system  of  grouping  analogous  to 
that  which  exists  among  organisms  in  general,  and  which  is 


THE    ARGUMENTS    FROM    CLASSIFICATION.  359 

explained  on  the  supposition  of  a  genealogical  tree  by  which 
all  organisms  are  affiliated.  If,  wherever  we  can  trace 
direct  descent,  multiplication,  and  divergence,  this  formatic  n 
of  groups  within  groups  takes  place ;  there  results  a  stron  g 
presumption  that  the  groups  within  groups  which  constitule 
the  animal  and  vegetal  kingdoms,  have  arisen  by  direct 
descent,  multiplication,  and  divergence — that  is,  by  evolu- 
tion. 

§  124.  Strong  confirmation  of  this  inference  is  furnished 
by  the  fact,  that  the  more  marked  differences  which  divide 
groups,  are,  in  both  cases,  distinguished  from  the  less 
marked  differences  which  divide  sub-groups,  by  this,  that 
they  are  not  simply  greater  in  degree,  but  they  are  more 
radical  in  hind.  Objects,  as  the  stars,  may  present  them- 
selves in  small  clusters,  which  are  again  more  or  less  aggre- 
gated into  clusters  of  clusters,  in  such  manner  that  the  in- 
dividuals of  each  simple  cluster,  are  much  closer  together 
than  are  the  simple  clusters  composing  a  compound  cluster  : 
in  which  case,  the  kinship  that  unites  groups  of  groups 
differs  from  the  kinship  that  unites  groups,  not  in  nature, 
but  only  in  amount.  But  this  is  not  the  case  either  with 
the  groups  and  sub-groups  which  we  know  have  resulted 
from  evolution,  or  with  those  which  we  here  infer  have  re- 
sulted from  evolution.  Among  these,  we  find  the  highest 
or  most  general  classes,  are  separated  from  one  another  by 
fundamental  differences  that  have  no  common  measure  with 
the  differences  that  separate  small  classes.  Observe  the  pa- 
rallelism. 

We  saw  that  each  sub-kingdom  of  animals  is  marked  o3 
from  the  other  sub-kingdoms,  by  a  total  unlikencss  in  its 
plan  of  organization :  that  is,  the  members  of  any  sub-kingdom 
are  bound  together,  not  by  some  superficial  attribute  which 
they  all  have,  but  by  some  attribute  determining  the  general 
nature  of  their  organizations.  While,  contrariwise,  the 
members  of  the  smallest  groups  are  united  together,  and  se- 
parated from  the  members  of  other  small  groups,  bv  modi- 


860  THE    EVOLUTION    OF    LIFE. 

fications  which  do  not  affect  the  essential  relations  of  parts. 
That  this  is  just  the  kind  of  arrangement  which  results  frora 
evolution,  the  case  of  languages  will  show. 

If  we  compare  the  dialects  spoken  in  different  parts  of 
England,  we  find  scarcely  any  differences  but  those  of  pro- 
nunciation :  the  structures  of  the  sentences  are  almost 
uuiform.  Between  English  and  the  allied  modern  languages, 
th  3re  are  decided  divergences  of  structure  :  there  are  some 
unlikenesses  of  idiom ;  some  unlikenesses  in  the  ways  of 
modifying  the  meanings  of  verbs  ;  and  considerable  unlike- 
nesses in  the  uses  of  genders.  But  these  unlikenesses  are  not 
sufficient  to  hide  a  general  community  of  organization.  A 
greater  contrast  of  structure  exists  between  these  modern  lan- 
guages of  Western  Europe,  and  the  classic  languages.  That 
differentiation  into  abstract  and  concrete  elements,  which  is 
shown  by  the  substitution  of  auxiliary  words  for  inflections, 
has  produced  a  higher  specialization  distinguishing  these 
languages  as  a  group  from  the  older  languages.  Neverthe- 
less, both  the  ancient  and  modern  languages  of  Europe,  to- 
gether with  some  Eastern  languages  derived  from  the  same 
original,  have,  under  all  their  differences  of  organization,  a 
fundamental  community  of  organization  ;  inasmuch  as  all  of 
them  exhibit  the  formation  of  words  by  such  a  coalescence 
and  integration  of  roots  as  destroys  the  independent  meanings 
of  the  roots.  These  Aryan  languages,  and  others  which 
have  the  amalgamate  character,  are  united  by  it  into  a  class 
distinguished  from  the  aptotic  and  agglutinate  languages  ;  in 
which  the  roots  are  eitLei  not  united  at  all,  or  so  incompletely 
united  that  one  of  them  still  retains  its  independent  meaning. 
And  philologists  find  that  these  fundamental  differences  which 
severally  determine  the  grammatical  forms,  or  modes  of  com- 
bining ideas,  are  really  characteristic  of  the  primary  divisions 
among  languages. 

That  is  to  say,  among  languages,  where  we  know  that 
evolution  has  been  going  on,  the  greatest  groups  are  marked 
off  frora  one  another  by  the  strongest  structural  contrasts  ; 
and  as  the  like  holds  among  groups  of  organisms,  there  re- 


THE    ARGUMENTS    FROM    CLASSIFICATION.  361 

Bulls  a   further  reason  for  inferring  that  these  have  been 
evolved. 

§  125.  There  is  yet  another  parallelism  of  like  meaning. 
We  saw  (§  101)  that  the  successively-subordinate  classes, 
orders,  genera,  and  species,  into  which  zoologists  and  botan- 
ists segregate  animals  and  plants,  have  not,  in  reality, 
those  definite  values  conventionally  given  to  them.  There  aro 
well-marked  species,  and  species  so  imperfectly  defined  that 
certain  systcmatists  regard  them  as  varieties.  Between 
genera,  strong  contrasts  exist  in  many  cases  ;  and  in  other 
cases,  contrasts  so  much  less  decided  as  to  leave  it  doubtful 
whether  they  constitute  generic  distinctions.  So,  too,  is  it 
with  orders  and  classes  :  in  some  of  which  there  have  been 
introduced  intermediate  sub-divisions,  having  no  equivalents 
in  others.  Even  of  the  sub- kingdoms  the  same  truth  holds. 
The  contrast  between  the  Molluscoida  and  the  Mollusca,  is  far 
less  than  that  between  the  Mollusca  and  the  Annulosa  ;  and 
there  are  naturalists  who  think  that  the  Fertebrata  are  so 
much  more  widely  separated  from  the  other  sub-kingdoms, 
than  these  are  from  one  another,  that  the  Vertehrata  should 
have  a  classificatory  value  equal  to  that  of  all  the  other  sub- 
kingdoms  taken  together. 

Now  just  this  same  indefinitcness  of  value,  or  incomplete- 
ness of  equivalence,  is  observable  in  those  simple  and  com- 
pound and  re-compound  groups,  which  we  see  arising  by 
evolution.  In  every  case,  the  endeavour  to  arrange  the 
divergent  products  of  evolution,  is  met  by  a  difficidty  like 
that  which  would  meet  the  endeavour  to  classify  the 
branches  of  a  tree,  into  branches  of  the  first,  second,  third, 
fourth,  &c,  orders — the  difficulty,  namely,  that  branches  of 
intermediate  degrees  of  composition  exist.  The  illustration 
furnished  by  languages  will  serve  us  once  more.  Some  dia- 
lects of  English  are  but  little  contrasted ;  others  are  strongly 
contrasted.  The  alliances  of  the  several  Scandinavian  tongues 
with  one  another  are  different  in  degree.  Dutch  is  much 
24 


362  THE   EVOLUTION    OF   LIFE 

less  distinct  from  German  than  Swedish  is  ;  while  between 
the  Danish  and  Swedish  there  is  so  close  a  kinship,  that  they 
might  almost  be  regarded  as  widely- divergent  dialects. 
Similarly  on  comparing  the  larger  divisions,  we  see  that 
the  various  languages  of  the  Aryan  stock,  have  deviated 
from  the  original  to  very  unlike  distances.  The  geneial 
conclusion  is  manifest.  While  the  kinds  of  human  speech 
fall  into  groups,  and  sub-groups,  and  sub-sub-groups ;  yet 
the  groups  are  not  equal  to  one  another  in  value,  nor  have 
the  sub-groups  equal  values,  nor  the  sub-sub-groups. 

If,  then,  the  classification  of  organisms  results  in  several 
orders  of  assemblages,  such  that  assemblages  of  the  same 
order  are  but  indefinitely  equivalent ;  and  if,  where 
evolution  is  known  to  have  taken  place,  there  have  arisen 
assemblages  between  which  the  equivalence  is  similarly  in- 
definite ;  there  is  additional  reason  for  inferring  that 
organisms  are  products  of  evolution. 

§  126.  A  fact  of  much  significance  remains.  If  groups 
of  organic  forms  have  arisen  by  divergence  and  re-diver- 
gence ;  and  if,  while  the  groups  have  been  developing 
from  simple  groups  into  compound  groups,  each  group  and 
sub-group  has  been  giving  origin  to  more  complex  forms 
of  its  own  type ;  then  it  is  inferable  that  there  once  ex- 
isted greater  structural  likenesses  between  the  members  of 
allied  groups,  than  exist  now.  Hence,  if  we  take  the 
simplest  members  of  any  group  to  be  those  which  have 
undergone  the  least  change  ;  we  may  expect  to  find  a  greater 
likeness  between  them  and  the  simplest  members  of  an  allied 
group,  than  we  find  between  the  more  complex  members 
of  the  two  groups.  This,  speaking  generally,  proves  to 
be  so. 

Between  the  sub-kingdoms,  the  gaps  are  extremely  wide  ; 
but  such  distant  kinships  as  may  be  discerned,  bear  out  an- 
ticipation. Speaking  of  that  extremely-degraded  vertebrate 
animal  the  Arrvphioxus,  which  has  several  molluscous  traits 


THE    ARGUMENTS    FROM    CLASSIFICATION.  363 

in  its  organization,  Dr  Carpenter  remarks,  that  it  "  furnishes 
an  apt  illustration  of  another  important  fact,  that  it  is  by 
the  lowest  rather  than  by  the  highest  forms  of  two  natural 
groups,  that  they  are  brought  into  closest  relation."  What 
are  the  faint  traces  of  community  between  the  Annulosa  and 
ihe  Mollusca  ?  They  are  the  thread-cells  which  some  of 
their  inferior  groups  have  in  common  with  the  Coelenterata. 
More  decided  approximations  exist  between  the  lower 
members  of  classes.  In  tracing  down  the  Crustacea  and 
the  Arachnida  from  their  more  complex  to  their  simpler 
forms,  zoologists  meet  with  difficulties  :  respecting  some  of 
these  simpler  forms,  it  becomes  a  question  which  class  they 
belong  to.  The  Lepidosiren,  about  which  there  have  been 
disputes  whether  it  is  a  fish  or  an  amphibian,  is  inferior  in  the 
organization  of  its  skeleton,  to  the  great  majority  of  both 
fishes  and  amphibia.  Widely  as  they  differ  from  them,  the 
lower  mammals  have  some  characters  in  common  with  birds, 
which  the  higher  mammals  do  not  possess. 

Now  since  this  kind  of  relationship  of  groups  is  not  ac- 
counted for  by  any  other  hypothesis,  while  the  hypothesis  of 
evolution  gives  us  a  clue  to  it ;  we  must  include  it  among  the 
evidences  of  this  hypothesis,  which  the  facts  of  classification 
furnish. 

§  127.  What  shall  we  say  of  these  several  leading  truths 
when  taken  together  ?  That  naturalists  have  been  gradually 
sompellcd  to  arrange  organisms  in  groups  within  groups ; 
and  that  this  is  the  arrangement  which  we  see  arises  by 
descent,  alike  in  individual  families  and  among  races  of  men, 
is  a  striking  circumstance.  That  while  the  smallest  groups 
are  the  most  nearly  related,  there  exist  beween  the  great 
sub-kingdoms,  structural  contrasts  of  the  profoundest  kind ; 
cannot  but  impress  us  as  remarkable,  when  we  see  that  where 
it  is  known  to  take  place,  evolution  actually  produces  these 
feebly-distinguished  small  groups,  and  these  strongly-dis- 
tinguished great  groups.     The  impression  made  by  these  two 


364  THE    EVOLUTION    OF    LIFE. 

parallelisms,  which,  add  meaning  to  each  other,  is  deepened 
by  the  third  parallelism,  which  enforces  the  meaning  of  both 
— the  parallelism,  namely,  that  as,  between  the  species, 
genera,  orders,  classes,  &c,  which  naturalists  have  formed, 
there  are  transitional  gradations ;  so  between  the  groups, 
sub-groups,  and  sub-sub-groups,  which  we  know  to  have 
been  evolved,  groups  of  intermediate  values  exist.  And 
these  three  correspondences  between  the  known  results  of 
evolution,  and  the  results  here  ascribed  to  evolution,  have 
further  weight  given  to  them  by  the  circumstance,  that  the 
kinship  of  groups  through  their  lowest  members,  is  just  the 
kinship  which  the  hypothesis  of  evolution  implies. 

Even  in  the  absence  of  these  specific  agreements,  the  broad 
fact  of  unity  amid  multiformity,  which  organisms  so  strik- 
ingly display,  is  strongly  suggestive  of  evolution.  Freeing 
ourselves  from  pre-conceptions,  we  shall  see  good  reason  to 
think  with  Mr  Darwin,  "  that  propinquity  of  descent — the 
only  known  cause  of  the  similarity  of  organic  beings — is  the 
bond,  hidden  as  it  is  by  various  degrees  of  modification,  which 
is  partly  revealed  to  us  by  our  classifications."  "When  we 
consider  that  this  only  known  cause  of  similarity,  joined  with 
the  only  known  cause  of  divergence,  which  we  have  in  the 
influence  of  conditions,  gives  us  a  key  to  these  likenesses 
obscured  by  unKken  esses,  to  which  no  consistent  interpreta- 
tion can  otherwise  be  given,  even  if  purely  hypothetical 
causes  be  admitted;  we  shall  see  that  were  there  none  of 
those  very  remarkable  harmonies  above  pointed  out,  the 
truths  of  classification  would  still  yield  strong  support  to  oui 
conclusion. 


CHAPTEE  V. 

THE  ARGUMENTS  FROM  EMBRYOLOGY. 

§  123.  There  was  briefly  set  forth  in  §  52,  a  remarkable 
induction  established  by  Von  Baer  ;  who  "  found  that  in  its 
earliest  stage,  every  organism  has  the  greatest  number  of 
characters  in  common  with  all  other  organisms  in  their 
earliest  stages  ;  that  at  a  stage  somewhat  later,  its  structure 
is  like  the  structures  displayed  at  corresponding  phases  by  a 
less  extensive  multitude  of  organisms  ;  that  at  each  subse- 
quent stage,  traits  are  acquired  which  successively  distin- 
guish the  developing  embryo  from  groups  of  embryos  that  it 
previously  resembled — thus  step  by  step  diminishing  the 
class  of  embryos  which  it  still  resembles ;  and  that  thus  the 
class  of  similar  forms  is  finally  narrowed  to  the  species  of 
which  it  is  a  member."  Though  this  generalization  is  to  be 
taken  with  qualifications,  yet,  as  an  average  truth,  it  may 
be  regarded  as  beyond  question ;  and  as  an  average  truth,  it 
has  a  profound  significance. 

For  if  we  follow  out  in  thought  the  implications 
of  this  truth — if  we  conceive  the  germs  of  all  kinds 
of  organisms  simultaneously  developing ;  if  after  taking 
their  first  step  together,  we  imagine  at  the  second  step,  one 
half  of  the  vast  multitude  diverging  from  the  other  half;  if, 
at  the  next  step,  we  mentally  watch  each  of  these  great 
assemblages  beginning  to  take  two  or  more  routes  of 
development ;  if  we  represent  to  ourselves  this  bifurcation 
simultaneously   going    on,    stage    after    stage,    in    all    the 


366  THE    EVOLUTION    OV    LIFE 

branches ;  we  shall  see  that  there  must  result  an  aggregate 
analogous,  in  its  arrangement  of  parts,  to  a  tree.  If  this  vast 
genealogical  tree  be  contemplated  as  a  whole,  made  up  of 
trunk,  great  branches,  secondary  branches,  and  so  on,  as  far 
as  the  terminal  twigs  ;  it  will  be  perceived  that  all  the 
various  kinds  of  organisms  represented  by  these  terminal 
twigs,  forming  the  periphery  of  the  tree,  will  stand  related  to 
each  other  in  small  groups,  which  are  united  into  groups  of 
groups,  and  so  on.  The  embryological  tree,  expressing  the 
developmental  relations  of  organisms,  will  be  similar  to  tho 
tree  which  symbolizes  their  classificatory  relations.  That 
subordination  of  classes,  orders,  genera,  and  species,  to  which 
naturalists  have  been  gradually  led,  is  just  that  subordination 
which  results  from  the  divergence  and  re-divergence  of 
embryos,  as  they  all  unfold.  On  the  hypothesis  of  evolution, 
this  parallelism  has  a  meaning — indicates  that  primordial 
kinship  of  all  organisms,  and  that  progressive  differentiation 
of  them,  which  the  hypothesis  alleges.  But  on  any  other 
hypothesis  the  parallelism  is  meaningless :  or  rather,  it 
raises  a  difficulty ;  since  it  implies  either  an  effect  without  a 
cause,  or  a  design  without  a  purpose. 

§  129.  It  was  said  above,  that  this  great  embryological 
law  is  to  be  taken  with  certain  qualifications.  The  resem- 
blances which  hold  together  great  groups  of  embryos  in  their 
early  stages,  and  which  hold  together  smaller  and  smaller 
groups  in  their  later  and  later  stages,  are  not  special  or 
exact,  but  general  or  approximate  ;  and  in  some  cases,  the 
conformity  to  this  general  law  is  very  imperfect.  These 
irregularities,  however,  instead  of  being  at  variance  with  the 
hypothesis  of  evolution,  afford  further  support  to  it. 

Observe,  first,  that  the  only  two  other  possible  suppositions 
respecting  developmental  changes,  are  negatived,  the  one  by 
this  general  law  and  the  other  by  the  minor  nonconformities 
to  it.  If  it  be  said  that  the  conditions  of  the  case  necessi- 
tated the  derivation  of  all  organisms  from  simple  gei-ms,  and 


THE    ARGUMENTS    FROM    EMBRYOLOGY.  367 

therefore  necessitated  a  morphological  unity  in  their  primitive 
states  ;  there  arises  the  obvious  answer,  that  the  morphologi- 
cal unity  thus  implied,  is  not  the  only  morphological  unity 
to  be  accounted  for.  Were  this  the  only  unity,  the  various 
kinds  of  organisms,  setting  out  from  a  common  primordial 
form,  should  all  begin  from  the  first  to  diverge  individually, 
as  so  many  radii  from  a  centre ;  which  they  do  not.  If,  other- 
wise, it  be  said  that  organisms  were  framed  upon  certain 
types,  and  that  those  of  the  same  type  continue  developing 
together  in  the  same  direction,  until  it  is  time  for  them  to 
begin  putting  on  their  specialities  of  structure  ;  then,  the 
answer  is,  that  when  they  do  finally  diverge,  they  ought 
severally  to  develop  in  direct  lines  towards  their  final  forms. 
No  reason  can  be  assigned  why,  having  once  parted  company, 
some  should  progress  towards  their  final  forms  by  irregular 
or  circuitous  routes.  On  the  hypothesis  of  design,  such  de- 
viations are  inexplicable. 

The  hypothesis  of  evolution,  however,  while  it  pre-supposes 
those  general  relations  among  embryos  which  are  found  tc 
exist,  also  affords  explanations  of  these  minor  nonconformities. 
If,  as  any  rational  theory  of  evolution  pre-supposes,  the  pro- 
gressive differentiations  of  organic  forms  from  one  another 
during  past  times,  have  resulted,  as  they  are  resulting  still, 
from  the  direct  and  indirect  effects  of  external  conditions — 
if  organisms  have  become  different,  either  by  immediate 
adaptations  to  unlike  habits  of  life,  or  by  the  mediate  adapta- 
tions resulting  from  preservation  of  the  individuals  most 
fitted  for  such  habits  of  life,  or  by  both  ;  and  if  the  embryonic 
changes  are  related  to  the  changes  that  were  undergone  by 
ancestral  races  ;  then  these  irregularities  must  be  expected. 
For  the  successive  changes  in  modes  of  life  pursued  by 
successive  ancestral  races,  can  have  had  no  regularity  of 
sequence.  In  some  cases  they  must  have  been  more  numerous 
than  in  others  ;  in  some  cases  they  must  have  been  greater 
in  degree  than  in  others ;  in  some  cases  they  must  have  been 
to  lower  modes,  in  some  cases  to  higher  modes,  and  in  some 


36S  THE   EVOLUTION    OF   LIFE. 

cases  to  modes  neither  higher  nor  lower.  Of  two  connate  racea 
which  diverged  in  the  remote  past,  the  one  may  have  had 
descendants  that  have  remained  tolerably  constant  in  theii 
habits,  while  the  other  niay  have  had  descendants  that  have 
passed  through  widely-aberrant  modes  of  life  ;  and  yet  some 
of  these  last  may  have  eventually  taken  to  modes  of  life  like 
those  of  the  divergent  races  derived  from  the  same  stock. 
And  if  the  metamorphoses  of  embryos,  indicate,  in  a  general 
way,  the  changes  of  structure  undergone  by  ancestors ;  then, 
the  later  embryologic  changes  of  such  two  allied  races,  will 
be  somewhat  different,  though  they  may  end  in  very  similar 
forms.  An  illustration  will  make  this  clear.  Mr  Darwin 
says  : — "  Petrels  are  the  most  aerial  and  oceanic  of  birds,  but 
in  the  quiet  sounds  of  Tierra  del  Fuego,  the  Pujjinuria 
berardl,  in  its  general  habits,  in  its  astonishing  power  of 
diving,  its  manner  of  swimming,  and  of  flying  when  un- 
willingly it  takes  flight,  would  be  mistaken  by  any  one  for 
an  auk  or  grebe  ;  nevertheless,  it  is  essentially  a  petrel,  but 
with  many  parts  of  its  organization  profoundly  modified." 
Now  if  we  suppose  these  grebe-like  habits  to  be  continued 
through  a  long  epoch,  the  petrel-form  to  be  still  more  ob- 
scured, and  the  approximation  to  the  grebe- form  still  closer ; 
it  is  manifest  that  while  the  chicks  of  the  grebe  and  the 
Pujjinuria  will,  during  their  early  stages  of  development, 
display  that  likeness  involved  by  their  common  derivation 
from  some  early  type  of  bird,  the  chick  of  the  Pujjinuria 
will  eventually  begin  to  show  deviations,  representative  of 
the  ancestral  petrel-structure,  and  will  afterwards  begin  to 
Lose  these  distinctions,  and  assume  the  grebe- structure. 

Hence,  remembering  the  perpetual  intrusions  of  organisms 
on  one  another's  modes  of  life,  often  widely  different ;  and 
remembering  that  these  intrusions  have  been  going  on  from 
the  beginning ;  we  shall  be  prepared  to  find  that  the  general 
Law  of  embryologic  parallelism,  is  qualified  by  irregularities 
that   are   mostly   small,    in   many   cases   considerable,    and 


THE    ARGUMENTS    FROM    EMBRYOLOGY.  36'.) 

occasionally  great.     The  hypothesis  of  evolution  accounts  for 
these  :  it  does  more — it  implies  the  necessity  of  them. 

§  130.  The  substitutions  of  organs  and  the  suppressions 
of  organs,  are  among  those  secondary  embryological  phe- 
nomena which  harmonize  with  the  belief  in  evolution 
but  cannot  be  reconciled  with  any  other  belief.  There  are 
cases  where,  during  its  earlier  stages  of  development,  an 
embryo  possesses  organs  that  afterwards  dwindle  away,  as 
there  arise  other  organs  to  discharge  the  same  functions. 
And  there  are  cases  where  organs  make  their  appearance, 
grow  to  certain  points,  have  no  functions  to  discharge,  and 
disappear  by  absorption. 

AVe  have  a  remarkable  instance  of  this  substitution  in  the 
successive  temporary  appliances  for  aerating  the  blood, 
which  the  mammalian  embryo  exhibits.  During  the  first 
phase  of  its  development,  the  mammalian  embryo  circulates 
its  blood  through  a  system  of  vessels  distributed  over  what 
is  called  the  area  vasculosa — a  system  of  vessels  homologous 
with  one  which,  among  fishes,  serves  for  aerating  the  blood 
until  the  permanent  respiratory  organs  come  into  play. 
After  a  time,  there  buds  out  from  the  mammalian  embryo,  a 
vascular  membrane  called  the  allantois,  homologous  with 
one  which,  in  birds  and  reptiles,  replaces  the  first  as  a 
breathing  apparatus.  But  while  in  the  higher  ovipai'ous 
vertebrates,  the  allantois  serves  the  purpose  of  a  lung  during 
the  rest  of  embryonic  life,  it  does  not  do  so  in  the  mamma- 
lian embryo.  In  implacental  mammals,  it  aborts,  having  no 
function  to  discharge ;  and  in  the  higher  mammals,  it 
becomes  "  placcntiferous,  and  serves  as  the  means  of  inter- 
communication between  the  parent  and  the  offspring  " — be- 
comes an  organ  of  nutrition  more  than  of  respiration.  Now 
since  the  first  system  of  external  blood-vessels,  not  being  in 
contact  with  a  directly-oxygenated  medium,  cannot  be  very 
serviceable  to  the  mammalian  embryo  as  a  lung ;  and  since 


<J70  THE   EVOLUTION   OF   LIFE. 

the  second  system  of  external  blood-vessels  is,  to  tho  im- 
placental  embryo,  of  no  greater  avail  than  the  first ;  and 
since  the  communication  between  the  embryo  and  the 
placenta  among  placental  mammals,  might  as  well  or  better 
have  been  made  directly,  instead  of  by  metamorphosis  oi 
the  allantois ;  these  substitutions  appear  unaccountable  as 
results  of  design.  But  they  are  quite  congruous  with  tho 
supposition,  that  the  mammalian  type  arose  out  of  lower 
vertebrate  types.  For  in  such  case,  the  mammalian  embryo, 
passing  through  states  representing,  more  or  less  distinctly, 
those  which  its  remote  ancestors  had  in  common  with  the 
lower  Vertebrata,  develops  these  subsidiary  organs  in  like 
ways  with  the  lower  Vertebrata. 

Even  more  striking  than  the  substitutions  of  organs  are 
the  suppressions  of  organs.  Mr  Darwin  names  some  cases 
as  "  extremely  curious ;  for  instance,  the  presence  of  teeth 
in  foetal  whales,  which  when  grown  up  have  not  a  tooth  in 
their  heads ;  *  *  *  It  has  even  been  stated  on  good 
authority  that  rudiments  of  teeth  can  be  detected  in  the 
beaks  of  certain  embryonic  birds."  Not  even  temporary 
functions  can  be  assigned  for  these  organs  that  are  first 
built  up  and  then  pulled  down  again.  -They  are  absolutely 
useless — their  formation  is  absolutely  superfluous.  Irrecon- 
cilable with  any  teleological  theory,  they  do  not  even  har- 
monize with  the  theory  of  fixed  types  which  are  maintained 
by  the  development  of  all  the  typical  parts,  even  where  not 
wanted ;  seeing  that  the  disappearance  of  these  incipient 
organs  during  foetal  life,  spoils  the  typical  resemblance. 
But  while  to  all  other  hypotheses  these  facts  are  stumbling- 
blocks,  they  yield  strong  support  to  the  hypothesis  of  evolu- 
tion. 

^-*" Allied  to  these  cases,  are  the  cases  of  what  has  been  called 
retrograde  development.  Many  parasitic  creatures  and 
creatures  which,  after  leading  active  lives  for  a  time,  eventu- 
ally become  fixed,  lose,  in  their  adult  states,  the  limbs  and 
senses  which  they  had  when  young.     It  moy  be  alleged- 


THE   ARGUMENTS   FROM   EMBRYOLOGY.  t57l 

however,  that  these  creatures  could  not  secure  the  habitats 
needful  for  them,  without  possessing  during  their  larva] 
stages,  eyes  and  swimming  appendages  which  eventually 
become  useless  ;  that  though,  by  losing  these,  their  organiza* 
tion  retrogresses  in  one  direction,  it  progresses  in  another 
direction ;  and  that,  therefore,  they  do  not  exhibit  the  need- 
less development  of  a  higher  type  on  the  way  to  a  lower 
type.  Nevertheless  there  are  instances  of  a  descent  in 
organization,  following  an  apparently-superfluous  ascent. 
Mr  Darwin  says  that  in  some  genera  of  cirripedes,  "  the 
Larvae  become  developed  either  into  hermaphrodites  having 
the  ordinary  structure,  or  into  what  I  have  called  comple- 
mented males,  and  in  the  latter,  the  development  has 
assuredly  been  retrograde  ;  for  the  male  is  a  mere  sack,  which 
lives  for  a  short  time,  and  is  destitute  of  mouth,  stomach, 
or  other  organ  of  importance,  excepting  for  reproduc- 
tion." 

§  131.  Comparative  embryology  shows  us  that  besides 
substitutions  of  organs,  there  are  what  may  be  called  substi 
tuted  modes  of  development.  The  same  kind  of  structure 
is  not  always  produced  in  the  same  way ;  and  some  allied 
groups  of  organisms  have  modes  of  evolution  which  appear 
to  be  radically  contrasted.  The  two  modes  are  broadly  dis- 
tinguishable as  the  direct  and  the  indirect.  They  may 
severally  characterize  the  general  course  of  evolution  as  u 
whole,  and  the  course  of  evolution  in  particular  organs. 

Thus  in  the  immense  majority  of  articulate  animals, 
metamorphoses,  more  or  less  marked  and  more  or  less 
numerous,  are  passed  through  on  the  way  to  maturity.  The 
familiar  transformations  of  insects  show  us  how  circuitous  is 
the  route  by  which  the  embryo-form  arrives  at  the  adult  form, 
among  some  divisions  of  the  Articulata.  But  there  are 
other  divisions,  as  the  lower  Aracfaiida,  in  which  the  unfold- 
ing of  the  egg  into  the  adult  takes  place  in  tho  simplest 
manner  :  the  substance  grows  towards  its  appointed  shapt 


372  THE   EVOLUTION   OF   LIFE. 

by  tlie  shortest  route.  The  Mollusca  furnish  contrasts  which^ 
though  less  marked,  are  essentially  of  the  same  nature.  Among 
some  Gasteropods,  according  to  Vogt,  the  germ-mass,  after 
undergoing  its  earliest  changes  in  the  same  way  as  germ- 
masses  in  general,  begins  to  transform  itself  bodily  into  the 
finished  structure  :  in  one  part,  the  component  cells  coalesce 
lo  form  the  heart,  in  another  part  to  form  the  liver,  and  so 
on.  But  in  other  classes  of  molluscs,  as  the  Cephalopods, 
the  e?ubryo  is  moulded  out  of  the  blastoderm,  or  superficial 
layer  of  the  germ-mass ;  and  the  various  organs,  mostly  aris- 
ing out  of  this  blastoderm  by  a  process  of  budding,  reach 
their  ultimate  shapes  through  successive  modifications,  while 
they  grow  at  the  expense  of  the  nutriment  absorbed  from 
the  rest  of  the  germ-mass.  And  this  indirect  development 
is  universal  among  the  Vertebrata. 

Now  on  contemplating  in  their  ensemble,  the  facts  thus 
briefly  indicated,  we  may  trace  among  these  irregularities 
something  like  a  general  rule.  The  indirect  development 
characterizes  the  most-highly-organized  forms.  In  the 
sub-kingdom  Vertebrata,  which,  considered  as  a  whole,  stands 
far  above  the  rest  in  complexity,  the  development  is  uniformly 
indirect.  It  is  indirect  in  the  great  mass  of  the  Articulata. 
It  is  indirect  in  the  highest  Mollusca.  Conversely,  it  is  direct 
in  a  large  proportion  of  the  lower  types.  The  eggs  of 
Protozoa,  of  Coelenterata,  of  inferior  Annuloida,  originate  the 
respective  structures  proper  to  them,  by  transformations  that 
are  almost  immediate ;  each  of  the  cycle  of  forms  passed 
through,  is  assumed,  when  the  proper  time  comes,  in  the 
simplest  way;  and  where  they  multiply  by  budding,  the 
substance  of  the  bud  passes  by  as  short  a  process  as  may  be, 
into  the  finished  form.  Where  among  the  simpler  types  of 
animals,  the  evolution  is  indirect,  its  indirectness  generally 
appears  to  be  related  to  some  transitional  mode  of  life,  which 
the  larva  passes  through  on  its  way  to  maturity ;  and  where 
we  find  direct  evolution  among  the  more  complex  types,  it  is 


THE    ARGUMENTS    FROM   EMBRYOLOGY.  o~'<i 

in  their  most  degraded  members  :  instance  the  Aren't  among 
the  Articulata* 

We  have  before  found  that  the  facts  of  social  organization 
furnish  us  with  hints  towards  interpreting  the  phenomena 
exhibited  in  individual  organisms.  Let  us  see  whether 
analogies  hence  derived,  do  not  help  us  here.  A  factory,  or 
other  producing  establishment,  or  a  town  made  up  of  such 
establishments,  is  an  agency  for  elaborating  some  commodity 
consumed  by  society  at  large ;  and  may  be  regarded  as 
analogous  to  a  gland  or  viscus  in  an  individual  organism.  If, 
now,  we  inquire  what  is  the  primitive  mode  in  which  one  of 
these  producing  establishments  grows  up,  we  find  it  to  be 
this.  A  single  worker,  who  himself  sells  the  produce  of  his 
labour,  is  the  germ.  His  business  increasing,  he  employs 
helpers — his  sons  or  others  ;  and  having  done  this,  he  be- 
comes a  vendor  not  only  of  his  own  handiwork,  but  of  that 
of  others.  A  further  increase  of  his  business  compels  him  to 
multiply  his  assistants,  and  his  sale  grows  so  rapid  that  he  is 
obliged  to  confine  himself  to  the  process  of  selling ;  that  is, 
he  ceases  to  be  a  producer,  and  becomes  simply  a  channel 
through  which  the  produce  of  others  is  conveyed  to  the 
public.  Should  his  prosperity  rise  yet  higher,  he  finds  that 
he  is  unable  to  manage  even  the  sale  of  his  commodities,  and 
has  to  employ  others,  probably  of  his  own  family,  to  aid  him 
in  selling ;  that  is,  to  him  as  a  main  channel  are  now  added 
subordinate  channels  ;  and  so  on  continuously.  Moreover, 
*  It  may  be  urged  that  the  mode  of  development  is  obviously  related  to  the 
tize  of  the  mass  which  is  to  be  transformed  into  the  embryo.  Doubtless  it  is 
true  that  direct  transformation  is  characteristic  of  small  ova,  and  indirect  trans- 
formation of  large  ova  ;  and  some  such  connexion  may  be  necessary.  Very  pos- 
sibly that  polarity  of  the  physiological  units,  which  determines  the  specific  structure 
will  not  act  throughout  a  large  mass  in  such  way  as  to  transform  it  bodily  into 
the  specific  structure  ;  though  it  will  thus  act  throughout  a  small  mass.  But  that 
the  bulk  of  the  ovum  is  not  the  sole  cause  of  this  difference  of  method,  is  proved 
by  the  fact  that  in  some  cases  where  the  development  is  comparatively  direct,  as 
in  Acteon,  the  ovum  is  very  much  larger  than  in  cases  where  it  is  comparatively 
indirect,  as  in  minute  iueccte. 


374  TITE    EVOLUTION    OF    LIFE. 

when  there  grow  up  in  one  place,  as  a  Manchester  or  a 
Birmingham,  many  establishments  of  like  kind,  this  process 
is  carried  still  further.     There  arise  factors  and  agents,  who 
are  the  channels  through  which  are  transmitted  the  pro- 
duce of  many  mills ;    and  we  believe  that  primarily,  these 
factors  were  manufacturers  who  undertook  to   dispose  of  the 
produce  of  smaller  houses  as  well  as  their  own,  and  ultimately 
became  salesmen   only.       Now  this,  which  is  the  original 
mode  in   which   social   agencies  of  all   kinds  are  evolved, 
does   not  continue  to  be  the   mode.     There  is  a  tendency 
everywhere  manifested  to  substitute  a  direct  process  for  this 
indirect   process.      Manufacturing    establishments    are    no 
longer  commonly  developed  through  the  series  of  modifica- 
tions above  described ;  but  mostly  arise  by  the  immediate 
transformation  of  a  number  of  persons  into  master,  clerks, 
foremen,    workers,    &c.      Instead    of    business-partnerships 
being  formed,  as  they  originally  were,  by  some  slow  unob- 
trusive union  between  traders  and  their  sons  or  assistants ; 
we   now    have  joint-stock-companies   resulting   by   sudden 
metamorphoses  of  groups  of  citizens.     The  like  is  true  with 
larger  and  more  complex  social  agencies.     A  new  town  in 
the  United  States  arises  not  at  all  after  the  old  method  of 
gradual  accumulations  round  a  nucleus,  and  successive  small 
modifications  of  structure   accompanying   increase  of  size ; 
but  it  grows  up  over  a  large  area,  according  to  a  pre-deter- 
mined  plan ;  and  there  are  developed  at  the  outset,  those 
various  civil,  ecclesiastical,  and  industrial  centres,  which  the 
incipient   city  will   require.       Even   in   the   formation   of 
colonies  we  may  similarly  see,  that  the  whole  type  of  social 
organization  proper  to  the  race  from  which  the  colony  comes, 
begins  at  once  to  show  itself.   There  is  not  a  gradual  passing 
through  all  those  developmental  phases  passed  through  by 
the   mother- society ;    but   there   is  a   comparatively   direct 
transformation  of  the  assemblage  of  colonists,  into  a  social 
organism  allied  in  structure  to  the  social  organism  of  which 
it  was  au  offset. 


THE    ARGUMENT'S   FROM    EMBRYOLOGY.  375 

Let  us  now  return  to  the  development  of  individual 
organisms ;  carrying  back  this  idea  with  us.  On  the 
hypothesis  of  evolution,  all  organs  must  have  been  originally 
formed  after  the  indirect  method,  by  the  accumulation  of 
modifications  upon  modifications ;  and  if  the  development  of 
(he  embryo  repeats  the  development  of  ancestral  races, 
organs  must  be  thus  formed  in  the  embryo.  To  a  consider- 
able extent  they  are  thus  formed.  There  is  a  striking 
parallelism  between  the  mode  in  which,  as  above  described, 
manufacturing  agencies  are  originally  evolved,  and  the 
mode  in  which  secreting  organs  are  evolved.  Out  of  the 
group  of  bile-cells  forming  the  germ  of  the  liver,  some 
centrally-placed  ones,  lying  next  to  the  intestine,  are  trans- 
formed into  ducts  through  which  the  secretion  of  the  peri- 
pheral bile-cells  is  poured  into  the  intestine  ;  and  as  the  peri- 
pheral bile-cells  multiply,  there  similarly  arise  secondary 
ducts  emptying  themselves  into  the  main  ones  ;  tertiary  ones 
into  these ;  and  so  on.  But  while  in  this  and  in  other 
organs,  the  development  remains  in  a  great  degree  indhect  ; 
there  are  organs,  as  the  heart,  in  which  it  is  comparatively 
direct.  The  heart  of  the  vertebrate  enibiyo  does  not  arise 
from  a  bud  ;  but  it  is  first  traceable  as  an  aggregated  mass 
of  cells,  becoming  distinct  from  the  cells  amid  which  it  is 
imbedded :  its  transformation  into  a  contractile  chamber,  is 
effected  by  the  consolidation  of  its  outer  cells  while  its  inner 
cells  liquify.  And  the  comparatively  direct  development 
thus  displayed  in  some  organs  of  the  higher  embryos,  is,  as 
we  have  seen,  characteristic  of  the  entire  development  in 
many  lower  embryos. 

On  the  hypothesis  of  evolution,  the  direct  mode  of  de- 
velopment in  animals,  must  have  been  substituted  for  the 
indirect  mode ;  as  we  see  that  it  is  substituted  in  societies. 
How  comes  it  to  have  been  substituted  ?  By  studying  the 
cause  of  the  substitution  in  the  social  organism,  we  may 
perhaps  get  some  insight  into  its  cause  in  the  individual  or- 
ganism. The  direct  mode  of  forming  social  agencies 


376  THE    EVOLUTION    OF   LIFE. 

replaces  the  indirect  mode,  when  these  social  agencies  have 
either  been  so  long  established,  or  have  become  so  prevalent,  or 
both,  as  to  modify  the  people's  habits  and  ideas.  Groups 
of  citizens  unite  into  corporate  bodies  which  quickly  organ- 
ize, because  the  habit  of  forming  such  combinations  has  so 
far  modified  the  thoughts  and  feelings  of  citizens,  that  it 
becomes  natural  to  them  thus  to  arrange  themselves.  So 
too,  is  it  with  the  men  who  form  a  colony.  The  rapid  as- 
sumption by  them  of  a  social  structure,  as  similar  as  circum- 
stances permit  to  the  structure  of  the  mother- society,  is 
manifestly  due  to  the  fact,  that  the  organization  of  the 
mother-society  has  moulded  the  emotions  and  beliefs  of  its 
members  into  conformity  with  itself;  so  that  when  some  of 
its  members  are  transferred  to  a  colony,  they  arrange 
themselves  directly  into  a  structure  of  like  type  with  that 
of  the  mother-society :  they  do  not  repeat  all  the  stages 
through  which  the  mother- society  passed,  because  their 
natures  have  been  too  far  modified  to  allow  of  their  doing 
this.  That    action   and    reaction   between   a   social 

organism  and  its  units,  which  we  here  see  accounts  for 
changes  in  modes  of  social  development,  must  be  paralleled 
by  the  action  and  reaction  between  an  individual  organism 
and  its  units.  Various  classes  of  phenomena  compelled 
us  to  conclude,  that  each  kind  of  organism  is  composed  cf 
physiological  units,  having  certain  peculiarites  which  force 
them  to  arrange  themselves  into  the  form  of  the  species  to 
which  they  are  peculiar.  And  in  the  chapters  on  Genesis, 
Heredity,  and  Variation,  we  saw  reason  to  believe,  that 
while  the  polarities  of  the  physiological  units  determine  the 
structure  of  the  organism  as  a  whole;  the  organism  as  a 
whole,  if  its  structure  is  changed  by  incident  forces,  reacts 
on  the  physiological  units,  and  modifies  them  towards  con- 
formity with  its  new  structure.  Now  this  action  and  reac- 
tion between  an  organic  aggregate  and  its  units,  tending 
ever  to  bring  the  two  into  absolute  harmony,  must  be  con- 
tinually making  the  developmental   processes  more  direct ; 


THE    ARGUMENTS    FROM    EMBRYOLOGY.  377 

and  will  show  its  effects  in  all  kinds  of  ways  and  degree3, 
according  to  the  ancestral  history  of  each  species.  Suppos- 
ing it  were  possible  for  a  race  of  organisms  to  have  con- 
iraued  propagating  itself  through  an  indefinitely-long 
period  without  any  change  of  conditions,  necessitating 
change  of  structure ;  there  woidd  be  reached  so  complete  a 
iongruity  between  the  organic  aggregate  and  its  physiologi- 
cal units,  that  the  units  would  arrange  themselves  directly 
•nto  a  structure  like  that  of  the  adult  organism :  the  germ 
tvould  put  on  the  proper  characters  of  the  species,  with  little 
or  no  transposition  of  substance.  But  in  the  absence  of 
any  such  constancy  of  conditions  and  structure,  what  may  we 
expect  ?  "We  may  expect  that  where  the  conditions  and 
structure  have  been  most  constant,  the  mode  of  develop- 
ment will  be  the  most  direct ;  and  that  it  will  be  the  most 
indirect,  where  there  have  been  the  greatest  and  most 
numerous  changes  in  the  habits  and  structures  of  ancestral 
races  of  organisms.  And  we  may  also  expect  that  develop- 
mental changes  corresponding  to  early  ancestral  forms,  will 
undergo  an  obliteration  that  is  great  in  proportion  to  the 
fixity  of  organization  that  has  been  since  maintained.  The 
facts  appear  in  harmony  with  this  conclusion.  We  see  a 
comparatively-direct  development  in  those  inferior  tvpes  of 
animals,  which  show  us,  by  their  inferiority,  that  they  have 
not,  since  the  commencement  of  organic  life,  passed  through 
many  sets  of  changes.  And  where  we  find  direct  de- 
velopment among  higher  types  of  animals,  it  characterizes 
the  simpler  rather  than  the  more  complex  members  of  the 
types. 

Between  different  parts  in  the  same  embryo,  there  are  un- 
likenesses  in  the  method  of  formation,  which  seem  to  have 
kindred  meanings.  The  heart,  of  which  the  development  is 
in  great  measure  direct,  is  an  organ  that  appears  compara- 
tively early  among  the  ascending  grades  of  organic  forms ; 
and  having  appeared,  retains  throughout  the  character  of  a 
hollow  muscle.  Conversely,  the  organs  which  develop  with 
25 


378  THE    EVOLUTION    OF    LIFE. 

great  indirectness,  are  the  organs  of  external  relation , 
which,  in  the  progress  of  organic  forms,  undergo  varioua 
metamorphoses.  Some  light,  too,  is  thus  thrown  on 

certain  irregularities  in  the  order  of  development  of  organs. 
If  we  contemplate  those  continuous  actions  and  reactions 
which  tend  ever  to  establish  a  balance  between  an  organic 
aggregate  and  its  units  ;  we  shall  see  that  the  effect  which 
the  units  composing  any  organ,  produce  on  the  organism  as  a 
whole,  will  depend,  partly  on  the  permanence  of  such  organ, 
and  partly  on  its  proportional  mass.  The  influence  of  any 
force,  is  a  product  of  its  amount  multiplied  into  the  time  during 
which  it  has  acted.  Hence,  a  larger  part  of  the  aggregate 
acting  for  a  shorter  time,  will  impress  itself  on  the  phy- 
siological units,  as  much  as  a  smaller  part  acting  for  a 
longer  time  ;  and  may  thus  begin  to  show  its  influence  in 
the  developmental  changes,  as  soon  as,  or  even  earlier  than,  a 
part  that  has  existed  for  a  greater  period.  Thus  it  becomes 
comprehensible  why,  in  certain  Eatozoa  which  have  im- 
mensely-developed generative  systems,  the  rudiments  of  the 
generative  systems  are  the  first  to  become  visible.  And 
thus  are  also  explicable,  anomalies  such  as  those  pointed 
out  by  Prof.  Agassiz — the  appearance,  in  some  cases,  of 
traits  characterizing  the  species,  at  an  earlier  period  of 
development  than  traits  characterizing  the  genus. 

§  132.  So  that  while  the  embryologic  law  enunciated  by 
Von  Baer,  is  in  harmony  with  the  hypothesis  of  evolution, 
and  is,  indeed,  a  law  which  this  hypothesis  implies ;  the 
minor  nonconformities  to  the  law,  are  also  interpretable  by 
this  hypothesis.  Parallelism  between  the  courses  of  develop- 
ment in  species  that  had  a  common  ancestry,  is  liable  to  be 
variously  modified  in  correspondence  with  the  later  ancestral 
forms  passed  through  after  divergence  of  such  species.  The 
substitution  of  a  direct  for  an  indirect  process  of  formation, 
which  we  have  reason  to  believe  will  show  itself,  both  in  the 
unfolding  of  the  entire  organism  and  in  the  unfolding  of  par* 


THE   ARGUMENTS    FROM    EMBRYOLOGY.  '67V 

ticular  organs,  niust  obscure  the  enibryologic  history.  And 
the  parts  influencing  the  whole  in  degrees  varying  with  their 
masses,  there  results  a  further  influence  which,  from  the  out- 
set, must  begin  to  modify  the  metamorphoses  of  each  kind  of 
embryo  ;  and  cause  it  to  show  incipient  divergences  from 
embryos  which  had  ancestral  histories  the  same  as  its  own. 
Thus  we  find  three  different  causes  conspiring  in  endless 
ways  and  degrees,  to  produce  deviations  from  the  general  law 
— causes  which  are  manifestly  capable  of  producing,  under 
special  conditions,  changes  in  apparent  contradiction  to  this 
law. 


CHAPTER  VI. 

THE    ARGUMENTS    FROM    MORPHOLOGY. 

§  133.  Leaving  out  of  consideration  the  parallelism  oi 
development  which  characterizes  organisms  belonging  to  each 
group,  that  community  of  plan  which  exists  among  them 
when  they  are  mature,  is  extremely  remarkable  and  extremely 
suggestive.  As  before  shown  (§  103),  neither  the  supposition 
that  these  combinations  of  attributes  which  unite  classes  are 
fortuitous,  nor  the  supposition  that  no  other  combinations 
were  practicable,  nor  the  supposition  of  adherence  to  pre- 
determined typical  plans,  suffices  to  explain  the  facts.  An 
instance  will  best  prepare  the  reader  for  seeing  the  true 
meaning  of  these  fundamental  likenesses. 

Under  the  immensely-varied  forms  of  insects,  greatly  elon- 
gated like  the  dragon-fly,  or  contracted  in  shape  like  the 
lady-bird,  winged  like  the  butterfly,  or  wingless  like  the 
flea,  we  find  this  character  in  common — there  are  primarily 
twenty  segments.  These  segments  may  be  distinctly  marked, 
or  they  may  be  so  fused  as  to  make  it  difficult  to  find  the 
divisions  between  them.  This  is  not  all.  It  has  been 
shown  that  the  same  number  of  segments  is  possessed  by  all 
the  Crustacea.  The  highly- consolidated  crab,  and  the  squilla 
with  its  long,  loosely -jointed  divisions,  are  composed  of  the 
same  number  of  somites.  Though,  in  the  higher  crustaceans, 
some  of  these  successive  indurated  rings,  forming  the  exo- 
skeleton,  are  never  more  than  partially  marked  off  from  each 


TilE    ARGUMENTS    FROM    MORPHOLOGY.  381 

other ;  yet  they  are  indentifiable  as  homologous  with 
segments,  which,  in  other  crustaceans,  are  definitely 
divided.  What,  now,  can   be  the  meaning  of  this 

community  of  structure  among  these  hundreds  of  thousands  of 
species  filling  the  air,  burrowing  in  the  earth,  swimming  in 
the  water,  creeping  about  among  the  sea- weed,  and  having 
such  enormous  differences  of  size,  outline,  and  substance,  as 
that  no  community  would  be  suspected  between  them  ?  Why 
under  the  down-covered  body  of  the  moth  and  under  the 
hard  wing-cases  of  the  beetle,  should  there  be  discovered  the 
same  number  of  divisions  as  in  the  calcareous  framework  of 
the  lobster  ?  It  cannot  be  by  chance  that  there  exist  just 
twenty  segments  in  all  these  hundreds  of  thousands  of  species. 
There  is  no  reason  to  think  it  was  necessary,  in  the  sense 
that  no  other  number  would  have  made  a  possible  organism. 
And  to  say  that  it  is  the  result  of  design — to  say  that  the  Cre- 
ator followed  this  pattern  throughout,  merely  for  the  purpose 
of  maintaining  vhe  pattern — is  to  assign  a  motive  which,  if 
avowed  by  a  human  being,  we  should  call  whimsical.  No 
rational  interpretation  of  this  and  hosts  of  like  morphological 
truths,  can  be  given  except  by  the  hypothesis  of  evolution  ; 
and  from  the  hypothesis  of  evolution  they  are  corollaries. 
If  organic  forms  have  arisen  from  common  stocks  by  per- 
petual divergences  and  redivergcnces — if  they  have  continued 
to  inherit,  more  or  less  clearly,  the  characters  of  ancestral 
races;  then  there  will  naturally  result  these  communities  of 
fundamental  structure  among  extensive  assemblages  of  crea- 
tures, that  have  severally  become  modified  in  countless  ways 
and  degrees,  in  adaptation  to  their  respective  modes  of 
life.  To  this  let  it  be  added,  that  while  the  belief 

in  an  intentional  adhesion  to  a  pre-determincd  pattern 
throughout  a  whole  group,  is  totally  negatived  by  the  occur- 
rence of  occasional  deviations  from  the  pattern  ;  such  devi- 
ations are  reconcilable  with  the  belief  in  evolution.  As 
pointed  out  in  the  last  chapter,  there  is  reason  to  think  that 
remote  ancestral  traits,  will  be  obscured  more  or  less  according 


582  THE    EVOLUTION    OF     LIFE. 

as  the  superposed  modifications  of  structure,  have  or  have 
not  been  great  or  long  maintained.  Hence,  though  the  occur- 
rence of  articulate  animals,  such  as  spiders  and  mites,  having 
fewer  than  twenty  segments,  is  fatal  to  the  supposition  that 
twenty  segments  was  decided  on  for  the  three  groups  of 
superior  Articulata;  it  is  not  incongruous  with  the  supposition, 
that  some  primitive  race  of  articulate  animals,  bequeathed  to 
these  three  groups  this  common  typical  character — a  character 
which  has  nevertheless,  in  many  cases,  become  greatly  ob- 
scured, and  in  some  of  the  most  aberrant  orders  of  these 
classes,  quite  lost. 

§  134.  Besides  these  wide-embracing  and  often  deeply- 
hidden  homologies,  which  hold  together  different  animals, 
there  are  the  scarcery-less  significant  homologies  between 
different  organs  of  the  same  animal.  These  homologies, 
like  the  others,  are  obstacles  to  the  supernatural  interpreta- 
tions, and  supports  of  the  natural  interpretation. 

One  of  the  most  familiar  and  instructive  instances  is 
furnished  by  the  vertebral  column.  Snakes,  which  move 
sinuously  through  and  over  plants  and  stones,  obviously 
need  a  segmentation  of  the  bony  axis  from  end  to  end ;  and 
inasmuch  as  flexibility  is  required  throughout  the  whole 
length  of  the  body,  there  is  advantage  in  the  comparative 
uniformity  of  this  segmentation  :  the  creature's  movements 
would  be  impeded  if,  instead  of  a  chain  of  vertebrae  varying 
but  little  in  their  lengths,  there  existed  in  the  middle  of  the 
series  some  long  bony  mass  that  would  not  bend.  But  in  most 
of  the  higher  Fertebrata,  the  mechanical  actions  and  reac- 
tions demand  that  while  some  parts  of  the  vertebral  axis  shall 
be  flexible,  other  parts  shall  be  inflexible.  Inflexibility  is 
especially  requisite  in  that  part  of  the  vertebral  column 
called  the  sacrum ;  which,  in  mammals  and  birds,  forms  a 
fulcrum  exposed  to  the  greatest  strains  which  the  skeleton 
has  to  bear.  Now  in  both  mammals  and  birds,  this  rigid 
portion  of  the  vertebral  column  is  not  made  of  one  long 


THE   ARGUMENTS   FROM    MORPHOLOGY.  383 

segment  or  vertebra,  but  of  several  segments  fused  to- 
gether. In  man  there  are  five  of  these  confluent  sacral 
vertebrae  ;  and  in  the  ostrich  tribe  they  number  from  seven- 
teen to  twenty.  Why  is  this  ?  Why,  if  the  skeleton  of 
each  species  was  separately  contrived,  was  this  bony  mass 
made  by  soldering  together  a  number  of  vertebrae  like  those 
forming  the  rest  of  the  column,  instead  of  being  made  out  of 
one  simple  piece  ?  And  why,  if  typical  uniformity  was  to  be 
maintained,  does  the  number  of  sacral  vertebras  vary  within 
the  same  order  of  birds  ?  Why,  too,  should  the  develop- 
ment of  the  sacrum  be  by  the  round-about  process  of  first 
forming  its  separate  constituent  vertebrae,  and  then  de- 
stroying their  separateness  ?  In  the  embryo  of  a  mammal 
or  bird,  the  substance  of  the  vertebral  column  is,  at  the  out- 
set, continuous.  The  segments  that  are  to  become  vertebrae, 
arise  gradually  in  the  midst  of  this  originally-homogeneous 
axis.  Equally  in  those  parts  of  the  spine  which  are  to 
remain  flexible,  and  in  those  parts  which  are  to  grow 
rigid,  these  segments  are  formed  ;  and  that  part  of  the  spine 
which  is  to  compose  the  sacrum,  having  passed  out  of  its  ori- 
ginal unity  into  disunity,  by  separating  itself  into  segments, 
passes  again  into  unity  by  the  coalescence  of  these  segments. 
To  what  end  is  this  construction  and  re-construction  ?  If, 
originally,  the  spine  in  vertebrate  animals  consisted  from 
head  to  tail  of  separate  moveable  segments,  as  it  docs  still  in 
fishes  and  some  reptiles — if,  in  the  evolution  of  the  higher 
Vertcbrata,  certain  of  these  moveable  segments  were  ren- 
dered less  moveable  with  respect  to  each  other,  by  the 
mechanical  conditions  to  which  they  are  exposed,  and  at 
length  became  relatively  immoveable  ;  it  is  comprehensible 
why  the  sacrum  formed  out  of  them,  should  continue  ever 
after  to  show  more  or  less  clearly  its  originally-segmented 
structure.  But  on  any  other  hypothesis,  this  segmented 
structure  is  inexplicable.  "We  see  the  same  law  in 

comparing  the  wonderfully  complex  jaws  and  legs  in  crusta- 
ceaus,"  says  Mr  Darwin  •  referring  to  the  well-known  fact 


384:  THE    EVOLUTION   OF    LIFE. 

that  those  numerous  lateral  appendages  which,  in  the  lowei 
crustaceans  most  of  them  serve  as  legs,  and  have  like  shapes^ 
are,  in  the  higher  crustaceans,  some  of  them  represented  by 
enormously-developed  claws,  and  others  by  variously-modi- 
fied foot-jaws.  "It  is  familiar  to  abnost  every  one,"  ho 
continues,  "  that  in  a  flower  the  relative  position  of  tho 
sepals,  petals,  stamens,  and  pistils,  as  well  as  their  intimate 
structure,  are  intelligible  on  the  view  that  they  consist  of 
metamorphosed  leaves  arranged  in  a  spire.  In  monstrous 
plants  we  often  get  direct  evidence  jof  the  possibility  of  one 
organ  being  transformed  into  another  ;  and  we  can  actually 
see  in  embryonic  crustaceans  and  in  many  other  animals,  and 
in  flowers,  that  organs,  which  when  mature  become  extremely 
different,  are  at  an  early  stage  of  growth  exactly  alike." 
*  *  *  "  Why  should  one  crustacean,  which  has  an.  ex- 
tremely complex  mouth  formed  of  many  parts,  consequently 
always  have  fewer  legs  ;  or  conversely,  those  with  many  legs 
have  simpler  mouths  ?  Why  should  the  sepals,  petals, 
stamens,  and  pistils  in  any  individual  flower,  though  fitted 
for  such  widely-different  purposes,  be  all  constructed  on  the 
same  pattern  ?  " 

To  these  and  countless  similar  questions,  the  theory  of 
evolution  furnishes  the  only  rational  answer.  In  the  course 
of  that  change  from  homogeneity  to  heterogeneity  of  struc- 
ture, displayed  in  evolution  under  every  form,  it  will  neces- 
sarily happen  that  from  organisms  made  up  of  numerous 
like  parts,  there  will  arise  organisms  made  up  of  parts  more 
and  more  unlike  :  which  unlike  parts  will  nevertheless  con- 
tinue to  bear  traces  of  their  primitive  likeness. 

§  135.  One  more  striking  morphological  fact,  near  akin 
to  some  of  the  facts  dwelt  on  in  the  last  chapter,  must  be 
here  set  down — the  frequent  occurrence,  in  adult  animals 
and  plants,  of  rudimentary  and  useless  organs,  which  are 
homologous  with  organs  that  are  developed  and  useful  in 
allied  animals  and  plants.     In  the  last  chapter  we  saw  that 


THE   ARGUMENTS   FHOM    MORPHOLOGY.  b85 

during  the  development  of  embryos,  there  often  arise  organs 
which  disappear  on  being  replaced  by  other  organs  dis- 
charging the  same  functions  in  different  ways  ;  and  that  in 
some  cases,  organs  develop  to  certain  points,  and  are  then 
re-absorbed  without  performing  any  functions.  But  very 
generally,  the  partially-developed  organs  are  retained 
throughout  life. 

The  osteology  of  the  higher  Fertcbrata,  supplies  abundant 
examples.  Vertebral  processes  which,  in  one  tribe,  are  fully 
formed  and  ossified  from  independent  centres,  are,  in  other 
tribes,  mere  tubercles  not  having  independent  centres  of 
ossification.  While  in  the  tail  of  this  animal,  the  vertebrae 
are  severally  composed  of  centrum  and  appendages,  in  the 
tail  of  that  animal,  they  are  simple  osseous  masses  without 
any  appendages  ;  and  in  another  animal,  they  have  lost  their 
individualities  by  coalescence  with  neighbouring  vertebrae 
into  a  rudimentary  tail.  From  the  structures  of  the  limbs, 
analogous  facts  are  cited  by  comparative  anatomists.  The 
undeveloped  state  of  certain  metacarpal  bones,  characterizes 
whole  groups  of  mammals.  In  one  case  we  find  the  normal 
number  of  digits ;  and,  in  another  case,  a  smaller  number 
with  an  atrophied  digit  to  make  out  the  complement.  Here  is 
a  digit  with  its  full  number  of  phalanges ;  and  there  a  digit  of 
winch  one  phalange  has  been  arrested  in  its  growth.  Still 
more  remarkable  are  the  instances  of  entire  limbs  being  rudi- 
mentary ;  as  in  certain  snakes,  which  have  hind  legs  hidden 
beneath  the  integument.  So,  too,  is  it  with  the  dermal  ap- 
pendages. Some  of  the  smooth-skinned  amphibia  have  scales 
buried  in  the  skin.  The  seal,  which  is  a  mammal  considerably 
modified  in  adaptation  to  an  aquatic  life,  and  which  uses  its 
feet  mainly  as  paddles,  has  toes  that  still  bear  external  nails  ; 
but  the  manatee,  which  is  a  much  more  transformed  main- 
raal,  has  nailless  paddles,  which,  when  the  skin  is  re- 
moved, are  said,  by  Humboldt,  to  display  rudimentary  nails 
at  the  ends  of  the  imbedded  digits.  Nearly  all  birds  are 
covered  with  developed  feathers,  severally  composed  of  a  shaft 


J386  THK    EVOLUTION    OF    LIFE. 

bearing  fibres,  each  of  which  again  bears  a  fringe  of  down. 
But  in  some  birds,  as  in  the  ostrich,  various  stages  of  arrested 
development  of  the  feathers  may  be  traced ;  beginning  with 
the  unusually-elaborated  feathers  of  the  tail,  and  ending  with 
those  about  the  beak,  which  are  reduced  to  simple  hairs.  Nor 
is  this  the  extreme  case.  In  the  Apteryx  we  see  the  whole 
of  the  feathers  ^educed  t<  a  hair-like  form.  Again,  the  hair 
which  commonly  covers  the  body  in  mammals,  is  compara- 
tively rudimentary  over  the  greater  part  of  the  human  body, 
and  is  in  some  parts  reduced  to  mere  down — down  which 
nevertheless  proves  itself  to  be  homologous  with  the  hair  of 
mammals  in  general,  by  occasionally  developing  into  the 
original  form.  Numerous  cases  of  aborted  organs  are  given 
by  Mr  Darwin,  of  which  a  few  may  be  here  added.  "  No- 
thing can  be  plainer,"  he  remarks,  "than  that  wings  are  formed 
for  flight,  yet  in  how  many  insects  do  we  see  wings  so  reduced 
in  size  as  to  be  utterly  incapable  of  flight,  and  not  rarely 
lying  under  wing-cases,  firmly  soldered  together?"  *  *  * 
"  In  plants  with  separated  sexes,  the  male  flowers  often  have 
a  rudiment  of  a  pistil ;  and  Kblreuter  found  that  by  crossing 
such  male  plants  with  an  hermaphrodite  species,  the  rudi- 
ment of  the  pistil  in  the  hybrid  offspring  was  much  increased 
in  size ;  and  this  shows  that  the  rudiment  and  the  perfect  pistil 
are  essentially  alike  in  nature."  And  then,  to  complete  the 
proof  that  these  undeveloped  parts  are  marks  of  descent  from 
races  in  which  they  were  developed,  there  are  not  a  few  direct 
experiences  of  this  relation.  "  We  have  plenty  of  cases  of 
rudimentary  organs  in  our  domestic  productions — as  the 
stump  of  a  tail  in  tailless  breeds — the  vestige  of  an  ear  in 
earless  breeds — the  re-appearance  of  minute  dangling  horns 
in  hornless  breeds  of  cattle." 

Here,  as  before,  the  teleological  doctrine  fails  utterly; 
for  these  rudimentary  organs  are  useless,  and  occasionally 
even  detrimental.  The  doctrine  of  typical  plans  is  equally 
out  of  court ;  for  while,  in  some  members  of  a  group,  rudi- 
mentary organs  completing  the  general  type  are  traceable, 


THE   ARGUMENTS    FROM    MORPHOLOGY.  387 

in  other  members  of  the  same  group,  such  organs  are  unre- 
presents  d.  There  remains  only  the  doctrine  of  evolution ; 
aud  to  this,  these  rudimentary  organs  offer  no  difficulties. 
On  the  contrary,  they  are  among  its  most  striking  evi- 
dences. 

S  136.  The  general  truths  of  morphology  thus  coincide  in 
tneir  implications.  Unity  of  type,  maintained  under  extreme 
dissimilarities  of  form  and  mode  of  life,  is  explicable  as  re- 
sulting from  descent  with  modification  ;  but  is  otherwise 
inexplicable.  The  likenesses  disguised  by  unlikenesses,  which 
the  comparative  anatomist  discovers  between  various  organs 
in  the  same  organism,  are  worse  than  meaningless  if  it  be 
supposed  that  organisms  were  severally  framed  as  we  now 
see  them  ;  but  they  fit  in  quite  harmoniously  with  the  belief, 
that  each  kind  of  organism  is  a  product  of  accumidated 
modifications  upon  modifications.  And  the  presence  in  all 
kinds  of  animals  and  plants,  of  functionally-useless  parts 
corresponding  to  parts  that  are  functionally-useful  in  allied 
animals  and  plants,  while  it  is  totally  incongruous  with  the 
belief  in  a  construction  of  each  organism  by  miraculous  in- 
terposition, is  just  what  we  are  led  to  expect  by  the  belief 
that  organisms  have  arisen  by  progression. 


CHAPTER   VII. 

THE    ARGUMENTS    FROM    DISTRIBUTION. 

§  137.  In  §§  105  and  106,  we  contemplated  the  phenomena 
of  distribution  in  Space.  The  general  conclusions  reached, 
in  great  part  based  on  the  evidence  brought  together  by  Mr 
Darwin,  were  that,  "  on  the  one  hand,  we  have  similarly-con 
ditioned,  and  sometimes  nearly-adjacent,  areas,  occupied  by 
quite  different  Faunas.  On  the  other  hand,  we  have  areas 
remote  from  each  other  in  latitude,  and  contrasted  in  soil  as 
well  as  climate,  which  are  occupied  by  closely-allied  Faunas." 
Whence  it  was  inferred  that  "  as  like  organisms  are  not  uni- 
versally, or  even  generally,  found  in  like  habitats ;  nor  very 
unlike  organisms,  in  very  unlike  habitats ;  there  is  no  manifest 
pre-determined  adaptation  of  the  organisms  to  the  habitats." 
In  other  words,  the  facts  of  distribution  in  Space,  do  not 
conform  to  the  hypothesis  of  design.  At  the  same 

time  we  saw  that  "  the  similar  areas  peopled  by  dissimilar 
forms,  are  those  between  which  there  are  impassable  barriers  ; 
while  the  dissimilar  areas  peopled  by  similar  forms,  are  those 
between  which  there  are  no  such  barriers ;"  and  these 
generalizations  appeared  to  be  in  harmony  with  the  abund- 
antly-illustrated  truth,  "  that  each  species  of  organism  tends 
ever  to  expand  its  sphere  of  existence — to  intrude  on  other 
areas,  other  modes  of  life,  other  media." 

By  way  of  showing  still  more  clearly  the  effects  of  this 
competition  among  races  of  organisms,  let  me  here  add  some 
recently-published  instances  of  the  usurpations  of  areas,  and 


THE    ARGUMENTS   FltOM   DISTRIBUTION.  389 

changes  of  distribution  hence  resulting.  In  the  Natural  His- 
tory Review  for  January,  1864,  Dr  Hooker  quotes  as  follows 
from,  some  New  Zealand  naturalists : — "You  would  be  surprised 
at  the  rapid  spread  of  European  and  other  foreign  plants  in 
this  country.  All  along  the  sides  of  the  main  lines  of  road 
through  the  plains,  a  Polygonum  (auiculare),  called  '  Cow 
Grass/  grows  most  luxuriantly,  the  roots  sometimes  two  feet 
in  depth,  and  the  plants  spreading  over  an  area  from  four  to 
five  feet  in  diameter.  The  dock  (Rumex  obtustfolius  or  it!, 
crisjjus)  is  to  be  found  in  every  river  bed,  extending  into  the 
valleys  of  the  mountain  rivers,  until  these  become  mere  tor- 
rents. The  sow-thistle  is  spread  all  over  the  country,  growing 
luxuriantly  nearly  up  to  G000  feet.  The  water-cress  increases 
in  our  still  rivers  to  such  an  extent,  as  to  threaten  to  choke 
them  altogether :  *  *  *  I  have  measured  stems  twelve  feet 
long  and  three-quarters  of  an  inch  in  diameter.  In  some  of 
the  mountain  districts,  where  the  soil  is  loose,  the  white  clover 
is  completely  displacing  the  native  grasses,  forming  a  close 
sward.  *  *  *  In  fact,  the  young  native  vegetation  appears 
to  shrink  from  competition  with  these  more  vigorous  in- 
truders." "  The  native  (Maori)  saying  is,  '  as  the  white 
man's  rat  has  driven  away  the  native  rat,  so  the  European 
fly  drives  away  our  own,  and  the  clover  kills  our  fern,  so 
will  the  Maoris  disappear  before  the  white  man  himself.' " 

Given  this  universal  tendency  of  the  superior  to  over- 
run the  habitats  of  the  inferior  ;  let  us  consider  what,  on  the 
hypothesis  of  evolution,  will  be  the  effects  on  the  geo- 
graphical relationships  of  species. 

§  138.  A  race  of  organisms  cannot  expand  its  sphere  of 
existence,  without  subjecting  itself  to  new  external  conditions. 
Those  of  its  members  which  spread  over  adjaceut  areas, 
inevitably  come  in  contact  with  circumstances  partially 
different  from  their  previous  circumstances ;  and  such  of 
them  as  adopt  the  habits  of  other  organisms,  necessarily 
experience  rc-actions  more  or  less  contrasted  with  the  re 


390  THE    EVOLUTION    OF    LIFE. 

actions  before  experienced.  Now  if  changes  of  organic 
structure  are  caused,  directly  or  indirectly,  by  changes  in 
the  incidence  of  forces  ;  there  must  result  unlikenesses  of 
structure  between  the  divisions  of  a  race  which  colonizes 
new  habitats.  Hence,  in  the  absence  of  obstacles  to  migra- 
tion, we  may  anticipate  manifest  kinships  between  the 
animals  and  plants  of  one  area,  and  those  of  areas  adjoining  it. 
This  inference  corresponds  with  an  induction  before  set 
down  (§  106).  In  addition  to  the  illustrations  of  it  already 
quoted  from  Mr  Darwin,  his  pages  furnish  others.  One  is 
that  species  which  inhabit  islands  are  habitually  allied  to 
species  which  inhabit  neighbouring  main  lands ;  and  an- 
other is  that  the  faunas  of  clustered  islands  show  marked 
similarities.  "  Thus  the  several  islands  of  the  Galapagos 
Archipelago  are  tenanted,"  says  Mr  Darwin,  "in  a  quite 
marvellous  manner,  by  very  closely  related  species ;  so  that 
the  inhabitants  of  each  separate  island,  though  mostly  dis- 
tinct, are  related  in  an  incomparably  closer  degree  to  each 
other  than  to  the  inhabitants  of  any  other  part  of  the  world." 
Mr  Wallace  has  traced  "  variation  as  specially  influenced  by 
locality  "  among  the  Papilionidce  inhabiting  the  East  Indian 
Archipelago  :  showing  how  "  the  species  and  varieties  of 
Celebes  possess  a  striking  character  in  the  form  of  the 
anterior  wings,  different  from  that  of  the  allied  species  and 
varieties  of  all  the  surrounding  islands  ; "  and  how  "  tailed 
species  in  India  and  the  western  islands  lose  their  tails  as 
they  spread  eastward  through  the  archipelago."  During 
his  travels  on  the  Upper  Amazons,  Mr  Bates  found  that 
"  the  greater  part  of  the  species  of  Ithomice  changed  from 
one  locality  to  another,  not  further  removed  than  100  to  200 
miles ;  "  that  "  many  of  these  local  species  have  the  appear- 
ance of  being  geographical  varieties ; "  and  that  in  some 
species  "  most  of  the  local  varieties  are  connected  with  their 
parent  form  by  individuals  exhibiting  all  the  shades  of 
variation." 

Further    general    relationships    are   to   be   inferred.       If 


THE    ARGUMENTS    FROM    DISTRIBUTION.  391 

luces  of  organisms,  ever  being  thrust  by  pressure  of  popula- 
tion into  new  habitats,  undergo  modifications  of  structure  as 
they  diverge  more  and  more  widely  in  space,  it  follows  that, 
speaking  generally,  the  widest  divergences  in  Space  will 
indicate  the  longest  periods  during  which  the  descendants 
from  a  common  stock  have  been  subject  to  modifying  con- 
ditions ;  and  hence  that,  among  organisms  of  the  same 
group,  the  smaller  constrasts  of  structure  will  be  limited 
to  the  smaller  areas.  This  we  find :  "  varieties  being,'' 
as  Dr  Hooker  says  in  his  Flora  of  Tasmania,  "more  re- 
stricted in  locality  than  species,  and  these  again  than 
genera."  Again,  if  races  of  organisms  spread,  and 

as  they  spread  are  altered  by  changing  incident  forces  ;  it 
follows  that  where  the  incident  forces  vary  greatly  within 
given  areas,  the  alterations  will  be  more  numerous  than  in 
equal  areas  which  are  less- variously  conditioned.  This,  too, 
proves  to  be  the  fact.  Dr  Hooker  points  out  that  the  most 
uniform  regions  have  the  fewest  species ;  while  in  the  most, 
multiform  regions  the  species  are  the  most  numerous. 

§  139.  Let  us  consider  next,  how  the  hypothesis  of 
evolution  corresponds  with  the  facts  of  distribution,  not  over 
different  areas,  but  through  different  media.  If  all  forms  of 
organisms  have  descended  from  some  primordial  simplest 
form,  it  follows  that,  since  this  primordial  simplest  form 
must  have  inhabited  some  one  medium  out  of  the  several 
media  which  organisms  now  inhabit,  the  peopling  of  other 
media  by  its  descendants,  implies  migration  from  one 
medium  to  others — implies  adaptations  to  media  quite  unlike 
the  original  medium.  To  speak  specifically — water  being 
the  medium  in  which  the  lowest  living  forms  exist,  it  is 
implied  that  the  earth  and  the  air  have  been  colonized  from 
the  water.  Great  difficulties  appear  to  stand  in  the  way  of 
this  assumption.  Ridiculing  those  who  contend  for  the  uni- 
serial  development  of  organic  forms,  who  have,  indeed,  laid 
themselves  open   to   ridicule  by  their  many  untenable  pro- 


392  THE   EVOLUTION    OF    LIFE. 

positions,  Von  Baer  writes — "A  fish,  swimming  towards 
the  shore,  desires  to  take  a  walk,  but  finds  his  fins  useless. 
They  diminish  in  breadth  for  want  of  use,  and  at  the  same 
time  elongate.  This  goes  on  with  children  and  grandchil- 
dren for  a  few  millions  of  years,  and  at  last  who  can  be  as- 
tonished that  the  fins  become  feet  ?  It  is  still  more  natural 
",hat  the  fish  in  the  meadow,  finding  no  water,  should  gape 
after  air,  thereby,  in  a  like  period  of  time  developing 
lungs ;  the  only  difficulty  being  that  in  the  meanwhile, 
a  few  generations  must  manage  without  breathing  at 
all."  Though,    as   thus   presented,  the   belief  in   a 

transition  looks  laughable  ;  and  though  such  derivation  of 
terrestrial  vertebrates  by  direct  modification  of  the  piscine 
type,  is  untenable  ;  yet  we  must  not  therefore  conclude  that 
no  migrations  of  the  kind  alleged  can  have  taken  place. 
The  adage  that  "  truth  is  stranger  than  fiction,"  applies  quite 
as  much  to  Nature  in  general  as  to  human  life.  Besides  the 
fact  that  there  are  certain  fish  which  actually  do  "  take  a 
walk "  without  any  very  obvious  reason ;  and  besides  the 
fact  that  sundry  fish  ramble  about  on  land  when  impelled 
to  do  so  by  the  drying- up  of  the  waters  inhabited  by  them  ; 
there  is  the  still  more  astounding  fact,  that  one  kind  of  fish 
climbs  trees.  Few  things  seem  more  obviously  impossible, 
than  that  a  water-breathing  creature  without  efficient  linibs> 
should  ascend  eight  or  ten  feet  up  the  trunk  of  a  palm  ;  and 
yet  the  Andbas  scandens  does  as  much.  To  previous  testi- 
monies on  this  point,  Capt.  Mitchell  has  recently  added 
others.  Such  remarkable  cases  of  temporary  changes  of 
media,  will  prepare  us  for  conceiving  how,  under  special  con- 
ditions, permanent  changes  of  media  may  have  taken  place ; 
and  for  considering  how  the  doctrine  of  evolution  is  eluci 
dated  by  them. 

Both  marine  organisms  and  fresh-water  organisms,  are 
many  of  them  left  from  time  to  time  partially  or  completely 
without  water  ;  and  the  creatures  which  show  the  power  to 
change  their  media  temporarily  or  permanently,  are   in  very 


THE    ARGUMENTS    i  ROM   DISTRIBUTION.  393 

many  cases,  of  the  kinds  mo3t  liable  to  be  thus  deserted  by 
their  medium.  Let  us  consider  what  the  sea-shore  shows 
us.  Twice  a-day  the  rise  and  the  fall  of  the  tide., 

covers  and  uncovers  countless  plants  and  animals,  fixed  and 
moving  ;  and  through  the  alternation  of  spring  and  neap 
tides,  it  residts  that  the  exposure  of  the  organisms  living  low 
down  on  the  beach,  varies  both  in  frequency  and  duration  : 
while  some  of  them  are  left  dry  only  once  a  fortnight  for  a 
very  short  time,  others  a  little  higher  up,  are  left  dry  during 
two  or  three  hours  at  several  ebb  tides  every  fortnight. 
Then  by  small  gradations  we  come  to  such  as,  living  at  the 
top  of  the  beach,  are  bathed  by  salt-water  only  at  long  in- 
tervals ;  and  still  higher  to  some  which  are  but  occasionally 
splashed  in  stormy  weather.  "What,  now,  do  we  find  among 
the  organisms  thus  subject  to  various  regular  and  irregular 
alternations  of  media  ?  Besides  many  plants  and  many  fixed 
animals,  we  find  numerous  moving  animals  ;  some  of  which 
are  confined  to  the  lower  zones  of  this  littoral  region,  but  others 
of  which  wander  over  the  whole  of  it.  Omitting  the  humbler 
animal  forms,  it  will  suffice  to  observe  that  each  of  the  two 
great  sub-kingdoms,  Mollusca  and  Articulata,  supplies  ex- 
amples of  creatures  having  a  wide  excursiveness  within  this 
region.  "We  have  gasteropods  which,  when  the  tide  is  down, 
habitually  creep  snail-like  over  sand  and  sea- weed,  even  up  as 
far  as  high- water  mark.  We  have  several  kinds  of  crustaceans, 
of  which  the  crab  is  the  most  conspicuous,  running  about  on 
the  wet  beach,  and  sometimes  rambling  beyond  the  reach  of 
the  water.  And  then  note  the  striking  fact,  that  each  of  these 
forms  thus  habituated  to  changes  of  media,  is  allied  to  forms 
that  are  mainly  or  wholly  terrestrial.  On  the  West  Coast  of 
Ireland,  marine  gasteropods  are  found  on  the  rocks  three  hun- 
dred feet  above  the  sea,  where  they  are  only  at  long  intervals 
wetted  by  the  spray ;  and  though  between  gasteropods  of  this 
class  and  land- gasteropods  the  differences  are  considerable,  yet 
the  land-gasteropods  are  more  closely  allied  to  them  than  to 
any  other  Mollusca.  Similarly,  the  two  highest  orders  of 
2G 


394  the  evolution  or  life. 

crustaceans  have  their  species  which  live  occasionally,  or 
almost  entirely,  out  of  the  water :  there  is  a  kind  of  lobster 
in  the  Mauritius  which  climbs  trees ;  and  there  is  the  land- 
crab  of  the  West  Indies,  which  deserts  the  sea  when  it  reaches 
maturity,  and  re- visits  it  only  to  spawn.  Seeing,  thus,  how 
there  are  many  kinds  of  marine  creatures  whose  habitat 
habitually  exposes  them  to  changes  of  media ;  how  some  of 
the  higher  kinds  so  circumstanced,  show  a  considerable  adapt- 
ation to  both  media ;  and  how  these  amphibious  kinds  are 
allied  to  kinds  that  are  mainly  or  wholly  terrestrial ;  we 
shall  see  that  the  migrations  from  one  medium  to  another, 
which  evolution  pre- supposes,  are  by  no  means  impracticable. 
With  such  evidence  before  us,  the  assumption  that  the  dis- 
tribution of  the  Vertehrata  through  media  so  different  as  air 
and  water,  may  have  been  gradually  effected  in  some  analogous 
manner,  would  not  be  altogether  unwarranted,  even  had  we 
no  clue  to  the  process.  We  shall  find,  however,  a  tolerably 
distinct  clue.  Though  rivers,  and  lakes,  and  pools, 

have  no  sensible  tidal  variations,  they  have  their  rises  and 
falls,  regular  and  irregular,  moderate  and  extreme.  Especially 
in  tropical  climates,  we  see  them  annually  full  for  a  certain 
number  of  months,  and  then  dwindling  away  and  drying  up. 
This  drying  up  may  reach  various  degrees,  and  last  for  various 
periods  :  it  may  go  to  the  extent  only  of  producing  a  liquid 
mud,  or  it  may  reduce  the  mud  to  a  hardened,  fissured  solid  ; 
it  may  last  for  a  day  or  two  or  for  months.  That  is  to  say, 
aquatic  forms  which  are  in  one  place  annually  subject  to  a 
slight  want  of  water  for  a  short  time,  are  elsewhere  subject 
to  greater  wants  for  longer  times :  we  have  gradations  of 
transition,  analogous  to  those  which  the  tides  furnish.  Now 
it  is  well  known  that  creatures  inhabiting  such  waters,  have, 
in  various  degrees,  powers  of  meeting  these  contingences. 
The  contained  fish  either  bury  themselves  in  the  mud 
when  the  dry  season  comes,  or  ramble  in  search  of  other 
waters.  This  is  proved  by  evidence  from  India,  Guiana,  Siam, 
Ceylon ;  and  some  of  these  fish,  as  the  Anabas  scandens,  are 


THE    ARGUMENTS   FROM    DISTRIBUTION.  SQft 

known  to  survive  for  days  out  of  the  water.     But  the  facts  of 
greatest   significance   are   furnished   by  an    allied   class   of 
Fertebrata,  almost  peculiar  to  habitats  of  this  kind.     The 
Amphibia  are  not,  like  fish,  habitually  found  in  waters  that 
are  never  partially  or  wholly  dried  up ;  but  they  nearly  all 
inhabit  waters  which,  at  certain  seasons,  evaporate,  in  great 
measure  or  completely — waters  in  which  most  kinds  of  fish 
cannot  exist.     And  what  are  the  leading  structural  traits  of 
these  Amphibia?      They  have  two   respiratory  systems — 
pulmonic  and  branchial — variously  developed   in  difierent 
orders  ;  and  they  have  two  or  four  limbs,  also  variously  de- 
veloped. Further  the  class  Amphibia  consists  of  two  groups, 
in  one  of  which  this  duality  of  the  respiratory  system  is 
permanent,  and  the  development  of  the  limbs  always  incom- 
plete ;  and  in  the  other  of  which  the  branchiae  disappear  as 
the  lungs  and  limbs  become  fully  developed.     The  lowest 
group,  the  Perennibranchiata,  have  organs  homologous  with 
the  air-bladders  of  fishes,   transformed  in  various  degrees 
into  lungs,  until  "  in  the  Siren,  the  pulmonic  respiration  is 
more  extensive  and  important  than  the  branchial ;  "  and  to 
these  creatures,  having  a  habitat  partially  aerial  and  partially 
aquatic,  there  are  at  the  same  time  supplied,  in  the  shallow 
water  covering  soft  mud,  the  mechanical  conditions  which 
render   swimming   difficult,   and   rudimentary  limbs  useful. 
In  the  higher  group,  the  Caducibranchiata,,  we  find  still  more 
suggestive  transformations.    Having  at  first  a  structure  re- 
sembling that  which  is  permanent  in  the  perennibranchiate 
amphibian,    the   larva   of  the  caducibranchiate  amphibian, 
pursues    for   a   time   a   similar   life;     but   eventually,    the 
changes  are  carried  further  in  the  same  direction :  the  respir- 
ation of  air,  originally  supplementary  to  the  respiration  of 
water,  predominates  over  it  more  and  more,  till  it  replaces  it 
entirely  ;  and  an  additional  pair  of  legs  is  produced.     This 
having  been  done,  the  creature  either  becomes,  like  the  Triton, 
one  which  quits  the  water  only  occasionally ;  or,  like  the 
Frog,  one  which  pursues  a  life  mainly  terrestrial,  and  returns 


396  THE    EVOLUi'ION    OF   LIFE. 

to  the  water  now  and  then.  Finally,  if  we  ask  under  what 
conditions  this  metamorphosis  of  a  water-breather  into  an 
air-breather  completes  itself,  the  answer  is — it  completes  it- 
self at  the  time  when  the  shallow  pools  inhabited  by  the 
larvae,  are  being  dried  up  by  the  summer's  sun.* 

See,  then,  how  significant  are  the  facts  when  thus  brought 
together.  There  are  particular  habitats  in  which  animals  are 
subject  to  changes  of  media.  In  such  habitats  exist  animals 
having,  in  various  degrees,  the  power  to  live  in  both  media, 
consequent  on  various  phases  of  transitional  organization. 
Near  akin  to  these  animals,  there  are  some  that,  after  passing 
their  early  lives  in  the  water,  acquire  more  completely  the 
structures  fitting  them  to  live  on  land,  to  which  they  then 
migrate.  Lastly,  we  have  closely-allied  creatures  like  the 
Surinam  toad  and  the  terrestrial  salamander,  which,  though 
they  belong  by  their  structures  to  the  class  Amphibia,  are 
not  amphibious  in  their  habits — creatures  the  larvae  of  which 
do  not  pass  their  early  lives  in  the  water,  and  yet  go  through 
these  same  metamorphoses  !  Must  we  then  think  that  the 
distribution  of  kindred  organisms  through  different  media, 
presents  an  insurmountable  difficulty  ?  On  the  contrary, 
with  facts  like  these  before  us,  the  evolution-hypothesis 
supplies  possible  interpretations  of  many  phenomena  that  are 
else  unaccountable.  Realizing  the  way  in  which  such  changes 
of  media  are  in  some  cases  gradually  imposed  by  physical 
conditions,  and  in  other  cases  voluntarily  commenced  and 
slowly  increased  in  the  search  after  food  ;  we  shall  begin  to 
understand  how,  in  the  course  of  evolution,  there  have  arisen 

*  While  these  pages  are  passing  through  the  press,  Dr  Hooker  has  obliged 
me  by  pointing  out,  that  "  plants  afford  many  excellent  examples  "  of  analogous 
transitions.  He  says  that  among  true  "  water  plants,"  there  are  found,  in  the 
same  species,  varieties  which  have  some  leaves  submerged  and  some  floating  ; 
other  varieties  in  which  they  are  all  floating ;  and  other  varieties  in  which  they 
are  all  submerged.  Further,  that  many  plants  characterized  by  floating  leaves, 
and  which  have  all  their  leaves  floating  when  they  grow  in  deeper  water,  are 
found  with  partly  aerial  leaves  when  they  grow  in  shallower  water ;  and  thai 
slsewhere  they  occur  in  almost  dry  soil  with  all  their  leaves  aerial. 


THE    ARGUMENTS    FROM    DISTRIBUTION.  397 

those  strange  obscurations  of  one  type  by  the  externals  oJ 
another  type.  When  we  see  land-birds  occasionally  feeding 
by  the  water-side,  and  then  learn  that  one  of  them,  the  water- 
ouzel,  an  "  anomalous  member  of  the  strictly  terrestrial 
thrush  family,  wholly  subsists  by  diving — grasping  the  stones 
with  its  feet  and  using  its  wings  under  water  " — we  are  en- 
abled  to  comprehend  how,  under  pressure  of  population, 
aqxiatic  habits  may  be  acquired  by  creatures  organized  for 
aerial  life  ;  and  how  there  may  eventually  arise  an  ornithic 
type,  in  which  the  traits  of  the  bird  are  very  much  disguised. 
Finding  among  mammals,  some  that  in  search  of  prey  or 
shelter,  have  taken  to  the  water  in  various  degrees,  we  shall 
cease  to  be  perplexed  on  discovering  the  mammalian  structure 
hidden  under  a  fish-Like  form,  as  it  is  in  the  Cetacea.  Grant 
that  there  has  ever  been  going  on  that  re-distribution  of 
organisms,  which  we  see  still  resulting  from  their  intrusions 
on  one  another's  areas,  media,  and  modes  of  life ;  and  we 
have  an  explanation  of  those  multitudinous  cases  in  which 
homologies  of  structure  are  complicated  with  analogies.  And 
while  it  accounts  for  the  occurrence  in  one  medium  of  or- 
ganic types  fundamentally  organized  for  another  medium, 
the  doctrine  of  evolution  accounts  also  for  the  accompany- 
ing unfitnesses.  Either  the  seal  has  descended  from  some 
mammal  which  little  by  little  became  aquatic  in  its  habits, 
in  which  case  the  structure  of  its  hind  limbs  has  a  mean- 
ing ;  or  else  it  was  specially  framed  for  its  present  habi- 
tat, in  which  case  the  structure  of  its  hind  limbs  is  incom- 
prehensible. 

§  140.  The  facts  respecting  distribution  in  Time,  which 
have  more  than  any  others  been  cited  both  in  proof  and  in 
disproof  of  evolution,  are  too  fragmentary  to  be  conclusive 
either  way.  Were  the  geological  record  complete,  or  did  it, 
as  both  TTniformitarians  and  Progressionists  have  habitually 
assumed,  give  us  traces  of  the  earliest  organic  forms  ;  the 
evidence  hence  derived,  for  or  against,  would  have  had  more 


398  THE  EVOLLXION  of  life. 

weight  than  any  other  evidence.  As  it  is,  all  we  can  do  is  to 
see  whether  such  fragmentary  evidence  as  remains,  is  con- 
gruous with  the  hypothesis. 

Palaeontology  has  shown  that  there  is  a  "  general  relation 
between  lapse  of  time  and  divergence  of  organic  forms  " 
(§  107) ;  and  that "  this  divergence  is  comparatively  slow  and 
continuous,  where  there  is  continuity  in  the  geological  forma- 
tions, but  is  sudden  and  comparatively  wide,  wherever  there 
occurs  a  great  break  in  the  succession  of  strata."  Now  this 
is  obviously  what  we  should  expect.  The  hypothesis  implies 
structural  changes  that  are  not  sudden  but  gradual.  Hence, 
where  conformable  strata  indicate  a  continuous  record,  we 
may  expect  to  find  successions  of  forms  only  slightly  different 
from  one  another ;  while  we  may  rationally  look  for  consider- 
able contrasts  between  the  groups  of  forms  fossilized  in  adjacent 
strata,  where  there  is  evidence  of  a  great  blank  in  the  record . 

The  permanent  disappearances  of  species,  of  genera,  and  of 
orders,  which  we  saw  to  be  a  fact  tolerably- well  established,  is 
also  a  fact  for  which  the  belief  in  evolution  prepares  us. 
If  later  organic  forms  have  in  all  cases  descended  from 
earlier  organic  forms,  and  have  diverged  during  their  descent, 
both  from  their  prototypes  and  from  one  another  ;  then  it 
obviously  follows,  that  such  of  them  as  become  extinct  at  any 
epoch,  will  never  re-appear  at  a  subsequent  epoch  ;  since 
there  can  never  again  arise  a  concurrence  and  succession  of 
conditions,  such  as  those  under  which  each  particular  type 
was  evolved. 

Though  comparisons  of  ancient  and  modern  organic  forms, 
prove  that  many  types  have  persisted  through  enormous 
periods  of  time,  without  undergoing  great  changes ;  it  wa« 
shown  that  such  comparisons  do  not  disprove  the  occur- 
rence in  organic  forms,  of  changes  great  enough  to  produce 
what  are  called  different  types.  The  result  of  inductive  in- 
quiry we  saw  to  be,  that  while  a  few  modern  higher  types 
yield  signs  of  having  been  developed  from  ancient  lower 
types  ;  and  while  there  are  many  modern  types  which  may 


THE    ARGUMENTS    FROM    DISTRIBUTION.  399 

have  been  thus  developed,  though  we  are  without  evidence  that 
they  have  been  so  ;  yet  that  "  any  admissible  hypothesis  of 
progressive  modification  must  be  compatible  with  persistence 
without  progression  through  indefinite  periods."  Now  these 
results  are  quite  congruous  with  the  hypothesis  of  evolution. 
As  rationally  interpreted,  evolution  must  in  all  cases  be 
understood  to  result,  directly  or  indirectly,  from  the  incidence 
of  forces.  If  there  are  no  changes  of  conditions,  entailing 
organic  changes,  organic  changes  are  not  to  be  expected. 
Only  in  organisms  which  fall  under  conditions,  in  conformity 
to  which  there  arise  additional  modifications  answering  to 
additional  needs,  will  there  be  that  increased  heterogeneity 
which  characterizes  higher  forms.  Hence,  though  the  facts 
of  palaeontology  cannot  be  held  to  prove  evolution,  yet  they 
are  in  harmony  with  it ;  and  some  few  of  them  yield  it 
support. 

§  141.  One  general  truth  respecting  distribution  in  Time, 
is,  however,  profoundly  significant.  If,  instead  of  contem- 
plating the  relations  among  past  forms  of  life  taken  by  them- 
selves, we  contemplate  the  relations  between  them  and  the 
forms  now  existing ;  we  find  a  connexion  which  is  in  perfect 
harmony  with  the  belief  in  evolution,  but  quite  irreconcil- 
able with  any  other  belief. 

Note,  first,  how  full  of  meaning  is  the  close  kinship  that 
exists  between  the  aggregate  of  organisms  now  living, 
and  the  aggregate  of  organisms  which  lived  in  the  most 
recent  geologic  times.  In  the  last-formed  strata,  nearly  all 
the  imbedded  remains  are  those  of  species  which  still  flourish. 
Strata  a  little  older,  contain  a  few  fossils  of  species  now  ex- 
tinct ;  though,  usually,  species  greatly  resembling  extant  ones- 
Of  the  remains  found  in  strata  of  still  earlier  date,  the  ex- 
tinct species  form  a  larger  per  centage  ;  and  the  differences  be- 
tween them  and  the  allied  species  now  living,  are  more  marked. 
That  is  to  say,  the  gradual  change  of  organic  types  in  Time, 
which  we  before  saw  is  indicated  by  the  geological  record,  ia 


400  THE   EVOLU'liON   OF   LIFE. 

equally  indicated  by  the  relation  between  existing  organic 
types  and  organic  types  of  the  epoch  preceding  our  own. 
The  evidence  completely  accords  with  the  belief  in  a  descent 
of  present  life  from  past  life.  Doubtless  such  a 

kinship  is  not  incongruous  with  the  doctrine  of  special  crea_ 
tions.  It  may  be  argued  that  the  introduction,  from  time  to 
time,  of  new  species  better  fitted  to  the  somewhat  changed 
conditions  of  the  Earth's  surface,  would  result  in  an  apparent 
alliance  between  our  living  Flora  and  Fauna,  and  the  Floras 
and  Faunas  that  lately  lived.  No  one  can  deny  it.  But  on 
passing  from  the  most  general  aspect  of  the  alliance,  to  its 
more  special  aspects,  we  shall  find  this  interpretation  com- 
pletely negatived. 

For  besides  a  close  kinship  between  the  aggregate  of  sur- 
viving forms  and  the  aggregate  of  forms  that  have  died  out 
in  recent  geologic  times  ;  there  is  a  peculiar  connexion  of 
like  nature  between  present  and  past  forms  in  each  great 
geographical  region.  The  instructive  fact  before  cited  from 
Mr  Darwin,  is  the  "  wonderful  relationship  in  the  same  con- 
tinent between  the  dead  and  the  living."  This  relationship 
is  not  explained  by  the  supposition  that  new  species  have 
been  at  intervals  supernaturally  placed  in  each  habitat,  as  the 
habitat  became  modified ;  since,  as  we  saw,  species  are  by  no 
means  uniformly  found  in  the  habitats  to  which  they  are  best 
adapted.  It  cannot  be  said  that  the  marsupials  imbedded  in 
recent  Australian  strata,  having  become  extinct  because  of 
unfitness  to  some  new  external  condition,  the  existing  mar- 
supials were  then  specially  created  to  fit  the  modified  en 
vironment  ;  since  sundry  animals  found  elsewhere,  aro 
so  much  more  completely  in  harmony  with  these  new 
Australian  conditions,  that,  when  taken  to  Australia,  they 
rapidly  extrude  the  marsupials.  While,  therefore,  the  simi- 
larity between  the  existing  Australian  Fauna  and  the  Fauna 
which  immediately  preceded  it  over  the  same  area,  is  just 
that  which  the  belief  in  evolution  leads  us  to  expect ;  it 
is   a  similarity  which  cannot   be  otherwise  accounted   for. 


THE   ARGUMENTS   FROM    DISTRIBUTION.  40! 

And  so  is  it  with  parallel  relations  in  New  Zealand,  in  South 
America,  and  in  Europe. 

§  142.  Given,  then,  that  pressure  which  species  exercise 
on  one  another,  in  consequence  of  the  universal  overfilling  of 
their  respective  habitats — given  the  resulting  tendency  to 
thrust  themselves  into  one  another's  areas,  and  media,  and 
modes  of  life,  along  such  lines  of  least  resistance  as  from 
time  to  time  are  found — given  besides  the  changes  in  modes 
of  life,  hence  arising,  those  other  changes  which  physical 
alterations  of  habitats  necessitate — given  the  structural 
modifications  directly  or  indirectly  produced  in  organisms 
by  modified  conditions  ;  and  the  facts  of  distribution  in 
Space  and  Time  are  accounted  for.  That  divergence  and  re- 
divergence  of  organic  forms,  which  we  saw  to  be  shadowed 
forth  by  the  truths  of  classification  and  the  truths  of  embry- 
ology, we  see  to  be  also  shadowed  forth  by  the  truths  of 
distribution.  If  that  aptitude  to  multiply,  to  spread,  to 
separate,  and  to  differentiate,  which  the  human  races  have  in 
all  times  shown,  be  a  tendency  common  to  races  in  general, 
as  we  have  ample  reason  to  assume ;  then  there  will  result 
that  kind  of  relation  among  the  species,  and  genera,  and 
orders,  peopling  the  Earth's  surface,  which  we  find  exists. 
Those  remarkable  identities  of  type  discovered  between  or- 
ganisms inhabiting  one  medium,  and  strangely-modified  or- 
ganisms inhabiting  another  medium,  are  at  the  same  time 
rendered  comprehensible.  And  the  appearances  and  disap- 
pearances of  species  which  the  geological  record  shows  us,  as 
well  as  the  connexions  between  successive  groups  of  species 
from  early  eras  down  to  our  own,  cease  to  be  inexplicable. 


CHAPTEE  VIII. 

nOW    IS    ORGANIC    EVOLUTION    CAUSED? 

§  143.  Already  it  has  been  necessary  to  speak  of  tho 
causes  of  organic  evolution  in  general  terms ;  and  now  we 
are  prepared  for  considering  them  specifically.  The  task 
before  us  is  to  deduce  the  leading  facts  of  organic  evolution, 
from  those  same  first  principles  which  evolution .  at  large 
conforms  to. 

Before  attempting  this,  however,  it  will  be  instructive  to 
glance  at  the  causes  of  organic  evolution  that  have  been 
from  time  to  time  alleged. 

§  144.  The  theory  that  plants  and  animals  of  all  kinds 
were  gradually  evolved,  seems  to  have  been  at  first  accom- 
panied only  by  the  vaguest  conception  of  cause — or  rather, 
by  no  conception  of  cause  properly  so  called,  but  only  by  the 
blank  form  of  a  conception.  One  of  the  earliest  who  in 
modern  times  (1735)  contended  that  organisms  are  indefi- 
nitely modifiable,  and  that  through  their  modifications  they 
have  become  adapted  to  various  modes  of  existence,  was 
De  Maillet.  But  though  De  Maillet  supposed  all  living 
beings  to  have  arisen  by  a  natural,  continuous  process,  ho 
does  not  appear  to  have  had  any  definite  idea  of  that  which 
determines  this  process.  In  1794,  in  his  Zoonomia, 

Dr  Darwin  gave  reasons   (sundry  of  them  valid    ones)  for 
believing   that   organized   beings   of  every  kiud,  have  de- 


HOW    IS   ORGANIC   EVOLUTION   CAUSED?  403 

ecended  from  one,  or  a  few,  primordial  germs  ;  and  along 
with  some  observable  causes  of  modification,  which  he  points 
out  as  aiding  the  developmental  process,  he  apparently 
ascribes  it,  in  part,  to  a  tendency  given  to  such  germ  or 
germs  when  created.  He  suggests  the  possibility  "  that  all 
warm-blooded  animals  have  arisen  from  one  living  filament, 
which  The  Great  First  Cause  endued  with  animality,  with 
the  power  of  acquiring  new  parts,  attended  with  new  pro- 
pensities, directed  by  irritations,  sensations,  volitions,  and 
associations  ;  and  thus  possessing  the  faculty  of  continuing 
to  improve  by  its  own  inherent  activity. "  In  this  passage 
we  see  the  idea  to  be,  that  evolution  is  pre-determined 
by  some  intrinsic  proclivity.  "It  is  curious,"  savs 

Mr  Charles  Darwin,  "  how  largely  my  grandfather,  Dr 
Erasmus  Darwin,  anticipated  the  erroneous  grounds  of 
opinion,  and  the  views  of  Lamarck."  One  of  the  anticipa- 
tions was  this  ascription  of  development  to  some  inherent 
tendency.  To  the  "  plan  general  de  la  nature,  et  sa  marche 
uniforme  dans  ses  operations,"  Lamarck  attributes  "  la 
progression  evidente  qui  existe  dans  la  composition  de 
l'organisation  des  animaux ;  "  and  "  la  gradation  reguliere 
qu'ils  devroient  offrir  dans  la  composition  de  leur  organ- 
isation," he  thinks  is  rendered  irregular  by  secondary 
causes.  Essentially  the  same  in  kind,  though  some- 

what different  in  form,  was  the  conception  put  forth  in  the 
Vestiges  of  Creation ;  the  author  of  which  contends  "  that 
the  several  series  of  animated  beings,  from  the  simplest  and 
oldest  up  to  the  highest  and  most  recent,  are,  under  the  pro- 
vidence of  God,  the  results,  first,  of  an  impulse  which  has 
been  imparted  to  the  forms  of  life,  advancing  them,  in  defi- 
nite times,  by  generation,  through  grades  of  organization 
terminating  in  the  highest  dicotyledons  and  vertebrata ; '' 
and  that  the  progression  resulting  from  these  impulses,  is 
modified  by  certain  other  causes.  The  broad  general  con- 
trasts between  lower  and  higher  forms  of  life,  are  regarded 
by  him  as  due  to  an  innate  aptitude  to  give  birth  to  forms 


104  THE    EVOLUTION    OF   LIFE. 

0/  more  perfect  structures.  The  last  to  re-emin* 

ciate  this  doctrine  has  been  Prof.  Owen ;  who  asserts  "  the 
axiom  of  the  continuous  operation  of  creative  power,  or  of 
the  ordained  becoming  of  living  things."  Though  these 
highly-general  expressions  do  not  suggest  any  very  definite 
idea,  yet  they  imply  the  belief  that  organic  progress  is  a 
result  of  some  in-dwelling  tendency  to  develop,  supernatur- 
ally  impressed  on  living  matter  at  the  outset — some  ever- 
acting  constructive  force,  which,  independently  of  other 
forces,  moulds  organisms  into  higher  and  higher  forms. 

In  whatever  way  it  is  formulated,  or  by  whatever  language 
it  is  obscured,  this  ascription  of  organic  evolution  to  some 
aptitude  naturally  possessed  by  organisms,  or  miraculously 
imposed  on  them,  is  unphilosophical.  It  is  one  of  those  ex- 
planations which  explains  nothing — a  shaping  of  ignorance 
into  the  semblance  of  knowledge.  The  cause  assigned  is  not 
a  true  cause — not  a  cause  assimilable  to  known  causes — not 
a  cause  that  can  be  anywhere  shown  to  produce  analogous 
effects.  It  is  a  cause  unrepresentable  in  thought :  one  of 
those  illegitimate  symbolic  conceptions  which  cannot  by  any 
mental  process  be  elaborated  into  a  real  conception.  In 
brief,  this  assumption  of  a  persistent  formative  power,  in- 
herent in  organisms,  and  making  them  unfold  into  higher 
forms,  is  an  assumption  no  more  tenable  than  the  assump- 
tion of  special  creations :  of  which,  indeed,  it  is  but  a  modi- 
fication ;  differing  only  by  the  fusion  of  separate  unknown 
processes  into  a  continuous  unknown  process. 

§  145.  Along  with  this  intrinsic  tendency  to  progress, 
supposed  to  be  primordially  impressed  on  them,  Dr  Darwin 
held  that  animals  have  a  capacity  for  being  modified  by  pro- 
cesses which  their  own  desires  initiate.  He  speaks  of 
powers  as  "excited  into  action  by  the  necessities  of  the 
creatures  which  possess  them,  and  on  which  their  existence 
depends ; "  and  more  specifically  he  says  that  "  from  their 
first  rudiment  or  primordium,  to  the  termination   of  th^ir 


HOW    IS   ORGANIC    EVOLUTION    CAUSED?  405 

lives,  all  animals  undergo  perpetual  transformations ;  which 
are  in  part  produced  by  their  own  exertions,  in  consequence 
of  their  desires  and  aversions,  of  their  pleasures  and  their 
pains,  or  of  irritations,  or  of  associations ;  and  many  of  these 
acquired  forms  or  properties  are  transmitted  to  their  pos- 
terity "  While  it  embodies  a  belief  for  which  a  great  deal 
is  to  be  said,  this  passage  involves  the  assumption  that, 
desires  and  aversions,  existing  before  experiences  of  the  ac- 
tions to  which  they  are  related,  were  the  originators  of  the 
actions,  and  therefore  of  the  structural  modifications  caused 
by  them.  In  his  JPhilosophie  Zoologique,  Lamarck 

much  more  specifically  asserts  "  le  sentiment  inte'rieur," 
to  be  in  all  creatures  that  have  developed  nervous  svs- 
tems,  an  independent  cause  of  those  changes  of  form  which 
are  due  to  the  exercise  of  organs :  distinguishing  it  from 
that  simple  irritability  possessed  by  inferior  animals,  which 
cannot  produce  what  we  call  a  desire  or  emotion ;  and 
holding  that  these  last,  along  with  all  "qui  manquent 
de  systeme  nerveux,  ne  vivent  qu'a  l'aide  des  excitations 
ijii'ils  recoiveut  de  l'exterieur."  Afterwards  he  says — "je 
reconnus  que  la  nature,  obligee  d'abord  d'emprunter  des 
milieux  environnans  la  puissance  excitahice  des  mouvemens 
vitaux  et  des  actions  des  animaux  imparfaits,  sut,  en  com- 
posant  de  plus  en  plus  1'organisation  animate,  transporter  cetto 
puissance  dans  l'interieur  meme  de  ces  etres,  et  qu'd  la  fin, 
elle  parvint  a  mettre  cette  meme  puissance  a  la  disposition 
de  l'individu."  And  still  more  definitely  he  contends  that 
if  one  considers  "  la  progression  qui  se  montre  dans  la  com- 
position de  1'organisation, "  *  *  *  "alors  on  eut  pu  aperce- 
voir  comment  les  besnins,  d'abord  reduits  a,  nullite,  et  dont 
le  nombre  ensuite  s'est  accru  graduellement,  ont  amene*  le 
penchant  aux  actions  propres  a  y  satisfaire;  comment  los 
actions  devenucs  habituelles  et  energiques,  ont  occasionne*  le 
developpement  des  organes  qui  les  executent." 

Now  though  this  conception  of  Lamarck  is  more  precisely 
etated,  and  worked  out  with  much  greater  elaboration  and 


406  THE    EVOLUTION    OF    LIFE. 

wider  knowledge  of  the  facts,  it  is  essentially  the  same  as 
that  of  Dr  Darwin ;  and  along  with  the  truth  it  contains, 
contains  also  the  same  error  more   distinctly  pronounced. 
Merely  noting  that  desires  or  wants,  acting  directly  only 
on  the  nervo-muscular  system,  can  have  no  immediate  in- 
fluence on  very  many  organs,  as  the  viscera,  or  such  external 
appendages  as  hair  and  feathers ;   and  observing,  further, 
that  even  some   parts  which   belong   to   the   apparatus  of 
external  action,  such  as  the  bones  of  the  skull,  cannot  be 
made  to  grow  by  increase  of  function  called  forth  by  desire ;  it 
will  suffice  to  point  out  that  the  difficulty  is  not  solved,  but 
simply  slurred-over,  when  needs  or  wants  are  introduced  as 
independent  causes  of  evolution.     True  though  it  is,  as  Dr 
Darwin  and  Lamarck  contend,  that  desires,  by  leading  to 
increased  actions  of  motor  organs,  may  induce  further  de- 
velopments of  such  organs ;  and  true  as  it  probably  is,  that 
the  modifications  hence  arising,  are  transmissible  to  offspring ; 
yet  there  remains  the  unanswered  question — Whence  do  these 
desires  originate  ?     The  transferrence  of  the  exciting  power 
from  the  exterior  to  the  interior,  as  described  by  Lamarck, 
begs  the  question.     How  comes  there  a  wish  to  perform  an 
action  not  before  performed  ?  Until  some  beneficial  result  has 
been  felt  from  going  through  certain  movements,  what  can 
suggest  the  execution  of  such  movements?     Every  desire 
consists  primarily  of  a  mental  representation  of  that  which 
is  desired,  and  secondarily  excites  a  mental  representation  of 
the  actions  by  which  it  is  attained ;  and  any  such  mental 
representations  of  the  end  and  the  means,  imply  antecedent 
experience  of  the  end  and  antecedent  use  of  the  means.     To 
assume  that  in  the  course  of  evolution  there  from  time  to 
time  arose  new  kinds  of  actions  dictated  by  new  desires,  is 
simply  to  remove  the  difficulty  a  step  back. 

§  146.  Changes  of  external  conditions  are  named  by  Dr 
Darwin,  as  causes  of  modifications  in  organisms.  Assigning, 
us  evidence  of  original  kinship,  that  marked  similarity  of 


HOW    IS   ORGANIC   EVOLUTION    CAUSED?  407 

type  which  exists  among  animals,  he  regards  then  devia- 
tions from  one  another,  as  caused  by  differences  in  their 
modes  of  life :  such  deviations  being  directly  adaptive. 
Enumerating  various  appliances  for  procuring  food,  he  says 
they  all  "  seem  to  have  been  gradually  produced  during  many 
generations  by  the  perpetual  endeavour  of  the  creatures  to 
supply  the  want  of  food,  and  to  have  been  delivered  to  their 
posterity  with  constant  improvement  of  them  for  the  pur- 
poses required."  And  the  creatures  possessing  these  va- 
rious appliances,  are  considered  as  having  been  rendered 
unlike,  by  seeking  for  food  in  unlike  ways.  As  illustrating 
the  alterations  wrought  by  changed  circumstances,  he  names 
the  acquired  characters  of  domestic  animals.  La- 

marck has  elaborated  the  same  view  in  detail :  using  for  the 
purpose,  with  great  ingenuity,  his  extensive  knowledge  of 
the  animal  kingdom.  From  a  passage  in  the  Avertissement, 
it  would  at  first  sight  seem,  that  he  looks  upon  direct  adapt- 
ation to  new  conditions,  as  the  chief  cause  of  evolution.  He 
says — "Je  regardai  comme  certain  que  le  mouvement  des 
fluides  dans  l'interieur  des  animaux,  mouvement  qui  c'est 
progressivement  accelere  avec  la  composition  plus  grande  de 
l'organisation ;  et  que  V influence  des  circonstances  nouvelles, 
a  mesure  que  les  animaux  s'y  exposerent  en  se  repandant 
dans  tous  les  lieux  habitables,  furent  les  deux  causes  g£n^- 
rales  qui  ont  amene  les  differens  animaux  a  l'etat  ou  nous  les 
voyons  actuellement."  But  elsewhere,  the  view  he  expresses 
appears  decidedly  different  from  this.  He  asserts  that  "dans 
sa  marche,  la  nature  a  commence,  et  recommence  encore  tous 
les  jours,  par  former  les  corps  organises  les  plus  simples ;  " 
and  that  "  les  premieres  ebauches  de  l'animal  et  du  vegetal 
£tant  formees  dans  les  lieux  et  les  circonstances  convenables, 
les  facultes  d'une  vie  commencante  et  d'un  mouvement  or- 
ganique  etabli,  ont  necessairement  developpe  peu  a  peu  les 
organes,  et  qu'avec  le  temps  elles  les  ont  diversifies  ainsi  que 
'  les  parties."  And  then,  further  on,  he  puts  in  italics  this 
proposition  : — "  La  progression  dans  la  composition  de  Vor* 


4-08  THE    EVOLUTION    OF    LIFE. 

ganisation  suhit,  ca  et  la,  dans  la  serie  generale  lies  animaux, 
des  anomalies  operees  par  V  influence  des  cir  con  stances  d*  habi- 
tation, et  par  celle  des  habitudes  contractees."  These,  and 
sundry  other  passages,  joined  with  his  general  scheme  of 
classification,  make  it  clear  that  Lamarck  conceived  adaptivo 
modification  to  be,  not  the  cause  of  progression,  but  the 
cause  of  irregularities  in  progression.  The  inherent  tend- 
ency which  organisms  have,  to  develop  into  more  perfect 
forms,  would,  according  to  him,  result  in  a  uniform  series  of 
forms ;  but  varieties  in  their  conditions  work  divergences  of 
structure,  which  break  up  the  series  into  groups :  groups 
which  he  nevertheless  places  in  uni-serial  order,  and  regards 
as  still  substantially  composing  an  ascending  succession. 

§  147.  These  speculations,  crude  as  they  may  be  considered, 
show  much  sagacity  in  their  respective  authors,  and  have 
done  good  service.  Without  embodying  the  truth  in  a  de- 
finite shape,  they  contain  adumbrations  of  it.  Not  directly, 
but  by  successive  approximations,  do  mankind  reach  correct 
conclusions ;  and  those  who  first  think  in  the  right  direction, 
loose  as  may  be  their  reasonings,  and  wide  of  the  mark  as 
their  inferences  may  be,  yield  indispensable  aid  by  framing 
provisional  conceptions,  and  giving  a  bent  to  inquiry. 

Contrasted  with  the  dogmas  of  his  age,  the  idea  of  De 
Maillet  was  a  great  advance.  Before  it  can  be  ascertained 
how  organized  beings  have  been  gradually  evolved,  there 
must  be  reached  the  conviction  that  they  have  been  gradu- 
ally evolved;  and  this  conviction  he  reached.  His  wild 
notions  as  to  the  way  in  which  natural  agencies  acted  in  the 
production  of  plants  and  animals,  must  not  make  us  forget 
the  merit  of  his  intuition  that  animals  and  plants  were  pro- 
duced by  natural  causes.  In  Dr  Darwin's  brief  ex- 
position, the  belief  in  a  progressive  genesis  of  organisms,  is 
joined  with  an  interpretation  having  considerable  definite- 
ness  and  coherence.  In  the  space  of  ten  pages  he  not  only 
indicates  several  of  the  leading  classes  of  facts  which  suppor' 


FTOW    IS   ORGANIC   EVOLUTION    CAUSED  4^0 

the  hypothesis  of  evolution,  but  he  does  something  towards 
elucidating  the  process  of  evolution.  His  reasonings  show 
us  an  unconscious  mingling  of  the  belief  in  a  supernaturally- 
impressed  tendency  to  develop,  with  the  belief  in  a  develop- 
ment arising  from  the  changing  incidence  of  conditions. 
Probably  had  he  pursued  the  inquiry  further,  this  last  belief 
would  have  grown  at  the  expense  of  the  first.  La- 

marck, in  elaborating  this  general  conception,  has  given 
greater  precision  to  both  its  truth  and  its  error.  Asserting 
the  same  imaginary  factors  and  the  same  real  factors,  he  has 
traced  out  their  supposed  actions  in  detail ;  and  has,  in  con- 
sequence, committed  himself  to  a  greater  number  of  un- 
tenable positions.  But  while,  in  trying  to  reconcile  the 
facts  with  a  theory  which  is  only  an  adumbration  of  the 
truth,  he  laid  himself  open  to  the  criticisms  of  his  con- 
temporaries ;  he  proved  himself  profounder  than  his  con- 
temporaries, by  seeing  that  evolution,  however  caused,  has 
been  going  on.  If  they  were  wise  in  not  indorsing  a  theory 
which  fails  to  account  for  a  great  part  of  the  facts ;  they 
were  unwise  in  ignoring  that  degree  of  congruity  with  the 
tacts,  which  shows  the  theory  to  contain  some  fundamental 
verity. 

Leaving  out,  however,  the  imaginary  factors  of  evolution 
which  these  speculations  allege,  and  looking  only  at  the  one 
actual  factor  which  Dr  Darwin  and  Lamarck  assign  as 
accounting  for  some  of  the  phenomena ;  it  is  manifest  from 
our  present  stand-point,  that  this,  so  far  as  it  is  a  cause  of 
evolution,  is  a  proximate  cause  and  not  an  ultimate  cause. 
To  say  that  functional  adaptation  to  conditions,  produces 
either  evolution  in  general,  or  the  irregularities  of  evolution, 
is  to  raise  the  further  question — why  is  there  a  functional 
adaptation  to  conditions  ? — why  do  use  and  disuse  generate 
appropriate  changes  of  structure  ?  Neither  this  nor  any  other 
interpretation  of  biologic  evolution  which  rests  simply  on  (he 
basis  of  biologic  induction,  is  an  ultimate  interpretation.  The 
biologic  induction  must  itself  be  interpreted.  Only  when 
27 


410  THE    EVOLUTION    OF   LIFE. 

the  process  of  evolution  of  organisms,  is  affiliated  on  the 
process  of  evolution  in  general,  can  it  be  truly  said  to  be 
explained.  The  thing  required  is  to  show  that  its  various 
results  are  corollaries  from  first  principles.  We  have  to 
reconcile  the  facts  with  the  universal  laws  of  the  redistribu- 
tion of  matter  and  motion. 


CHAPTER  IX. 

EXTERNAL    FACTOKS. 

^  148.  TVken  illustrating  the  rhythm  of  motion  (First 
Principles,  §  94)  it  was  pointed  out  that  besides  the  daily 
and  annual  alternations  in  the  quantities  of  light  and  heat 
which  any  portion  of  the  Earth's  surface  receives  from  the 
Sun,  there  are  alternations  which  require  immensely- greater 
periods  to  complete.  Reference  was  made  to  the  fact,  that 
"  every  planet,  during  a  certain  long  period,  presents  more  of 
its  northern  than  of  its  southern  hemisphere  to  the  Sun  at  the 
time  of  its  nearest  approach  to  him ;  and  then  again,  during 
a  like  period,  presents  more  of  its  southern  hemisphere  than 
of  its  northern — a  recurring  co-incidence  which,  though 
causing  in  some  planets  no  sensible  alterations  of  climate,  in- 
volves in  the  case  of  the  Earth  an  epoch  of  2.1,000  years, 
during  which  each  hemisphere  goes  through  a  cycle  of  tem- 
perate seasons,  and  seasons  that  are  extreme  in  their  heat 
and  cold."  Further,  it  was  pomted  out  that  there  is  a  varia- 
tion of  this  variation.  The  slow  rhythm  of  temperate  and  in- 
temperate climates,  which  takes  21,000  years  to  complete, 
h  self  undergoes  exaggeration  and  mitigation,  during  epochs 
(hat  are  far  longer.  The  Earth's  orbit  slowly  alters  in 
form :  now  approximating  to  a  circle ;  and  now  becoming 
more  eccentric.  During  the  period  at  which  the  Earth's 
orbit  has  least  eccentricity,  the  temperate  and  intemperate 
climates   which   repeat   their   cycle    in    21.000    years,    arc 


412  VHE   EVOLUTION    OF    LIFE. 

severally  less  temperate  and  less  intemperate,  than  when, 
some  one  or  two  millions  of  years  later,  the  Earth's  orbit  has 
reached  its  extreme  of  eccentricity. 

Thus,  besides  those  daily  variations  in  the  quantities  of  light 
and  heat  received  by  organisms,  and  responded  to  by  varia- 
tions in  their  functions ;  and  besides  the  annual  variations  in 
the  quantities  of  light  and  heat  which  organisms  receive, 
and  similarly  respond  to  by  variations  in  their  functions; 
there  are  variations  that  severally  complete  themselves  in 
21,000  years  and  in  some  millions  of  years — variations  to 
which  there  must  also  be  a  response  in  the  changed  functions 
of  organisms.  The  whole  vegetal  and  animal  kingdoms, 
are  subject  to  a  quadruply -compounded  rhythm  in  the  in- 
cidence of  the  forces  on  which  life  primarily  depends — a 
rhythm  so  involved  in  its  slow  working  round,  that  at 
no  time  during  one  of  these  vast  epochs,  can  the  in- 
cidence of  these  forces  be  exactly  the  same  as  at  any  other 
time.  To  the  direct  effects  so  produced  on  organ- 

isms, have  to  be  added  much  more  important  indirect  effects. 
Changes  of  distribution  must  result.  Certain  redistributions 
are  occasioned  even  by  the  annual  variations  in  the  quantities 
of  the  solar  rays  received  by  each  part  of  the  Earth's  surface. 
The  migrations  of  birds  thus  caused,  are  familiar.  So  too 
are  the  migrations  of  certain  fishes :  in  some  cases  from  one 
part  of  the  sea  to  another ;  and  in  some  cases  from  salt  water 
to  fresh  water.  Now  just  as  the  yearly  changes  in  the  amounts 
of  light  and  heat  falling  on  each  locality,  yearly  extend 
and  restrict  the  habitats  of  many  organisms  that  are  able  to 
move  about  with  some  rapidity ;  so  must  these  alternations 
of  temperate  and  intemperate  climates  produce  extensions 
and  restrictions  of  habitats.  These  extensions  and  restric- 
tions, though  slow,  will  be  universal — will  affect  the  habitats 
of  stationary  organisms  as  well  as  those  of  locomotive  ones. 
For  if  during  an  astronomic  era,  there  is  going  on  at  any 
limit  to  a  plant's  habitat,  a  diminution  of  the  winter's  cold 
or  summer's  heat,  which  had  before  stopped  its  spread  at 


EXTERNAL   FACTORS.  413 

that  limit;  then,  though  the  individual  plants  arc  fixed, 
yet  the  species  will  move  :  the  seeds  of  plants  living  at  the 
limit,  will  produce  individuals  that  survive  beyond  the  limit. 
The  gradual  spread  so  effected,  having  gone  on  for  some  ten 
thousand  years,  the  opposite  change  of  climate  will  begin  to 
cause  retreat :  the  tide  of  each  species  will  during  the  one 
half  of  a  long  epoch,  slowly  flow  into  new  regions,  and 
then  will  slowly  ebb  away  from  them.  Further,  this  rise 
and  fall  in  the  tide  of  each  species,  will,  during  far  longer 
intervals,  undergo  increasing  rises  and  falls  and  then  de- 
creasing  rises  and  falls.  There  will  be  an  alternation  of 
spring  tides  and  neap  tides,  answering  in  its  period  to  the 
changing  eccentricity  of  the  Earth's  orbit. 

These  astronomical  rhythms,  therefore,  entail  on  organisms 
unceasing  changes  in  the  incidence  of  forces  in  two  ways. 
They  directly  subject  them  to  variations  of  solar  influences, 
in  such  a  manner  that  each  generation  is  somewhat  differently 
affected  in  it3  functions ;  and  they  indirectly  bring  afbout 
complicated  alterations  in  the  environing  agencies,  by  carry- 
ing each  species  into  the  presence  of  new  physical  conditions. 

§  149.  The  power  of  geological  actions  to  modify  every- 
where the  circumstances  in  which  plants  and  animals  are 
placed,  is  conspicuous.  In  each  locality,  denudation  slowly 
uncovers  different  deposits ;  and  slowly  changes  the  exposed 
areas  of  deposits  already  uncovered.  Simultaneously,  the 
alluvial  beds  that  are  being  formed,  are  qualitatively  affected 
by  these  progressive  changes  in  the  natures  and  proportions  of 
the  strata  denuded.  The  inclinations  of  surfaces  and  their 
directions  with  respect  to  the  Sun,  are  at  the  same  time 
altered ;  and  the  organisms  existing  on  them  are  thus  having 
their  thermal  conditions  continually  altered,  as  well  as  their 
drainage.  Igneous  action,  too,  complicates  these  gradual 
modifications.  A  flat  region  cannot  be  step  by  step  thrust 
up  into  a  protuberance,  without  unlike  climatic  changes 
being  produced  in  its  several  parts  by  their  exposures  to  dif- 


414: 


THE   EVOLUTION    OF    LIFE. 


ferent  aspects.  Extrusions  of  trap,  wherever  they  take 
place,  revolutionize  the  localities ;  both  over  the  areas  covered, 
and  over  the  areas  on  which  their  detritus  is  left.  And 
where  volcanoes  are  formed,  the  ashes  they  occasionally  send 
out,  modify  the  character  of  the  soil  throughout  large  sur- 
rounding tracts. 

In  like  manner  alterations  in  the  Earth's  crust,  cause  the 
ocean  to  be  ever  subjecting  the  organisms  it  contains  to  new 
combinations  of  conditions.  Here  the  water  is  being  deep- 
ened by  subsidence,  and  there  shallowed  by  upheaval.  "While 
the  falling  upon  it  of  sediment  brought  down  by  neighbour- 
ing large  rivers,  is  raising  the  sea-bottom  in  one  place;  in 
another,  the  habitual  rush  of  the  tide  is  carrying  away  the 
sediment  previously  deposited.  The  mineral  character  of 
the  submerged  surface  on  which  sea- weeds  grow  and  molluscs 
crawl,  is  everywhere  occasionally  changed :  now  by  the 
bringing  away  from  an  adjacent  shore  some  previously  un- 
touched strata ;  and  now  by  the  accumulation  of  organic 
remains,  such  as  the  shells  of  pteropods  or  of  foraminifera. 
A  further  series  of  alterations  in  the  circumstances  of  marine 
organisms,  is  entailed  by  changes  in  the  movements  of  the 
water.  Each  modification  in  the  outlines  of  neighbouring 
shores,  makes  the  tidal  streams  vary  their  directions  or 
velocities,  or  both.  And  the  local  temperature  is  from  time 
to  time  raised  or  lowered,  because  some  far-distant  re-ar- 
rangement of  the  Earth's  crust,  has  wrought  a  divergence  in 
those  circulating  currents  of  warm  and  cold  water  which 
pervade  the  ocean. 

These  geologically-caused  changes  in  the  physical  charac- 
ters of  each  environment,  occur  in  ever-new  combinations,  and 
with  ever-increasing  complexity.  As  already  shown  (First 
Principles,  §  118),  it  follows  from  the  law  of  the  multiplication 
of  effects,  that  during  long  periods,  each  tract  of  the  Earth's 
surface  increases  in  heterogeneity  of  both  form  and  substance 
Hence  plants  and  animals  of  all  kinds,  are,  in  the  course  of 
generations,  subject  by  these  alterations  in  the  crust  of  the 


EXTERNAL    FACTORS. 


415 


Earth,  to  sets  of  incident  forces  which  differ  from  previous 
6ets,  both  by  changes  in  the  proportions  of  the  factors,  and, 
occasionally,  by  the  addition  of  new  factors. 

§  150.  Variations  in  the  astronomical  conditions  joined 
with  variations  in  the  geological  conditions,  bring  about 
variations  in  the  meteorological  conditions.  Those  extremely 
slow  alternations  of  elevation  and  subsidence,  which  there  is 
reason  to  believe  take  place  over  immense  areas,  here  pro- 
ducing a  continent  where  once  there  was  a  fathomless  ocean, 
and  there  causing  wide  seas  to  spread  where  in  a  long  past 
epoch  there  stood  snow-capped  mountains,  gradually  work 
great  atmospheric  changes.  While  yet  the  highest  parts  of 
an  emerging  surface  of  the  Earth's  crust,  exist  as  a  cluster  of 
islands,  the  plants  and  animals  which  in  course  of  time  migrate 
to  them,  have  climates  that  are  peculiar  to  small  tracts  of 
land  surrounded  by  large  tracts  of  water.  As,  by  successive 
upheavals,  greater  areas  are  exposed,  there  begin  to  arise 
sensible  contrasts  between  the  states  of  their  peripheral  parts 
and  their  central  parts :  the  sea  and  land  breezes,  which 
daily  moderate  the  extremes  of  temperature  near  the  shores, 
cease  to  affect  the  interiors  ;  and  the  interiors,  less  qualified 
too  in  their  heat  and  cold  by  such  ocean-currents  as  bathe 
the  shores,  acquire  more  decidedly  the  characters  due  to 
their  latitudes.  Along  with  the  further  elevations  which 
unite  the  members  of  the  archipelago  into  a  continent,  there 
come  new  meteorologie  changes,  as  well  as  exacerbations  of 
the  old.  The  winds,  which  were  comparatively  uniform  in 
their  directions  and  periods  when  only  islands  existed,  grow 
involved  in  their  distribution,  and  widely- different  in  dif- 
ferent parts  of  the  continent.  The  quantities  of  rain  which 
they  discharge  and  of  moisture  which  they  absorb,  vary 
everywhere  according  to  the  proximity  to  the  sea  and  to 
surfaces  of  land  having  special  characters. 

Other  complications  result  from  variations  of  height  above 
the  sea :  elevation  producing  a  decrease  of  heat  and  conse- 


416  THE   EVOLUTION    OF    LIFE. 

quentty  an  increase  in  the  precipitation  of  water — a  precipit- 
ation that  takes  the  shape  of  snow  where  the  elevation  is 
very  great,  and  of  rain  where  it  is  not  so  great.  The  gather- 
ing of  clouds  and  descent  of  showers  around  mountain  tops, 
are  familiar  to  every  tourist.  Inquiries  in  the  neighbouring 
valleys,  prove  that  within  distances  of  a  mile  or  two  the 
recurring  storms  differ  in  their  frequency  and  violence. 
Xay,  even  a  few  yards  off,  the  meteorologic  conditions  vary  in 
such  regions :  as  witness  the  way  in  which  the  condensing 
vapour  keeps  eddying  roimd  on  one  side  of  some  high  crag, 
while  the  oiher  side  is  clear ;  or  the  way  in  which  the  snow- 
line runs  irregularly  to  many  different  heights,  in  ail  the  minor 
valleys  and  ravines  and  hollows  of  each  mountain  side. 

Climatic  variations  that  are  thus  geologically  produced, 
being  compounded  with  those  which  result  from  the  slow 
astronomical  changes ;  and  no  correspondence  existing  be- 
tween the  geologic  and  the  astronomic  rhythms ;  it  results 
that  the  same  plexus  of  actions  never  recurs.  Hence  the 
incident  forces  to  which  the  organisms  of  every  locality  are 
exposed  by  atmospheric  agencies,  are  ever  passing  into  un- 
paralleled combinations ;  and  these  are  on  the  average  ever 
becoming  more  complex. 

§  151.  Besides  changes  in  the  incidence  of  inorganic 
forces,  there  are  equally  continuous,  and  still  more  involved, 
changes  in  the  incidence  of  forces  which  organisms  exercise 
on  one  another.  As  before  pointed  out  (§  105),  the  plants 
and  animals  inhabiting  each  locality,  are  held  together  in  so 
entangled  a  web  of  relations,  that  any  considerable  modifica- 
tion which  one  species  undergoes,  acts  indirectly  on  many 
other  species ;  and  eventually  changes,  in  some  degree,  the 
circumstances  of  nearly  all  the  rest.  If  an  increase  of  heat, 
or  modification  of  soil,  or  decrease  of  humidity,  causes  a  par- 
ticular kind  of  plant  either  to  thrive  or  to  dwindle ;  an 
unfavourable  or  favourable  effect  is  wrought  on  all  such 
competing  kinds  of  plants,  as  are  not  immediately  influenced 


EXTERNAL   FACTORS.  417 

in  the  same  way.  The  animals  which  eat  the  seeds  or  browse 
on  the  leaves  either  of  the  plant  primarily  affected  or  those  of 
its  competitors,  are  severally  altered  in  their  states  of  nutri- 
tion and  in  their  numbers ;  and  this  change  presently  tells 
on  various  predatory  animals  and  parasites.  And  since  each 
of  these  secondary  and  tertiary  changes,  becomes  itself  a- 
centre  of  others ;  the  increase  or  decrease  of  each  species, 
produces  "waves  of  influence  which  spread  and  reverberate 
and  re-reverberate,  throughout  the  whole  Flora  and  Fauna 
of  the  locality. 

More  marked  and  multiplied  still,  arc  the  ultimate  effects 
of  those  causes  •which  make  possible  the  colonization  of  neigh- 
bouring areas.  Each  intruding  plant  or  animal,  besides  the 
new  inorganic  conditions  to  which  it  is  subject,  is  subject  to 
organic  conditions  considerably  different  from  those  to  which 
it  has  been  habituated.  It  has  to  compete  with  some  organ- 
isms unlike  those  of  its  preceding  habitat.  It  must  preserve 
itself  from  enemies  not  before  encountered.  Or  it  may  meet 
with  a  species  over  which  it  has  some  advantage  greater 
than  any  that  it  had  over  the  species  it  was  previously  in 
contact  with.  Even  where  migration  does  not  bring  it  face 
to  face  with  new  competitors  or  new  enemies  or  new  prey, 
it  inevitably  experiences  new  proportions  among  these. 
Further,  an  expanding  species  is  almost  certain  to  invade 
more  than  one  adjacent  region.  Spreading  north  or  south,  it 
will  come  among  the  plants  and  animals,  here  of  a  level 
district  and  there  of  a  hilly  one — here  of  an  inland  tract, 
and  there  of  a  tract  bordered  by  the  sea.  And  while  differ- 
ent groups  of  its  members  'will  thus  expose  themselves  to 
the  actions  and  re-actions  of  different  Floras  and  Faunas, 
these  different  Floras  and  Faunas  will  simultaneously  have 
their  organic  conditions  changed  by  the  intruders. 

This  process  becomes  gradually  more  active  and  more- 
complicated.  Though  in  particular  cases,  a  plant  or  animal 
may  fall  into  simpler  relations  with  the  living  things  around, 
than  those  it  was  before  placed  in ;  yet  it  is  manifest  thut, 


418  THE    EVOLUTION   OF   LIFE. 

on  the  average,  the  organic  environments  of  organisms  have 
been  increasing  in  heterogeneity.  As  the  number  of  speciee 
with  which  each  species  is  directly  or  indirectly  implicated, 
multiplies,  each  species  is  oftener  subject  to  changes  in  the 
organic  actions  which  influence  it.  These  more  frequent 
changes  severally  grow  more  involved.  And  the  corre- 
sponding reactions  affect  larger  Floras  and  Faunas,  in  ways 
increasingly  complex  and  varied. 

§  152.  When  the  astronomic,  geologic,  meteorologic,  and 
organic  agencies  that  are  at  work  on  each  species  of  organ- 
ism, are  contemplated  as  becoming  severally  more  compli- 
cated in  themselves,  and  at  the  same  time  as  co-operating  in 
ways  that  are  always  more  or  less  new ;  it  will  be  seen  that 
throughout  all  time,  there  has  been  an  exposure  of  organisms 
to  endless  successions  of  modifying  causes  which  gradually 
acquire  an  intricacy  that  is  scarcely  conceivable.  Every 
kind  of  plant  and  animal  may  be  regarded  as  for  ever  pass- 
ing into  a  new  environment — as  perpetually  having  its 
relations  to  external  circumstances  altered,  either  by  their 
changes  with  respect  to  it  when  it  remains  stationary,  or  by 
its  changes  with  respect  to  them  when  it  migrates,  or  by 
both. 

Yet  a  further  cause  of  progressive  alteration  and  compli- 
cation in  the  incident  forces,  exists.  All  other  things  con- 
tinuing the  same,  every  additional  faculty  by  which  an 
organi&m  is  brought  into  relation  with  external  objects,  as 
well  as  every  improvement  in  such  faculty,  becomes  a  means 
of  subjecting  the  organism  to  a  greater  number  and  variety 
of  external  stimuli,  and  to  new  combinations  of  external 
stimuli.  So  that  each  advance  in  complexity  of  organization, 
itself  becomes  an  added  source  of  complexity  in  the  incidence 
of  external  forces. 

Once  more,  every  increase  in  the  locomotive  powers  of 
animals,  increases  both  the  multiplicity  and  the  multiformity 
of  tbe  actions  of  things  upon  them,  and  of  their  reactions 


EXTERNAL   FACTORS.  419 

upon  tilings.  Doubling  a  creature's  activity,  quadruples  the 
area  that  comes  within  the  range  of  its  excursions :  thus 
augmenting  in  number  and  heterogeneity,  the  external 
agencies  which  act  on  it  during  any  given  interval. 

By  compounding  the  actions  of  these  several  orders  of 
factors,  there  is  produced  a  geometric  progression  of  changes, 
increasing  with  immense  rapidity.  And  there  goes  on  an 
equally  rapid  increase  in  the  frequency  with  which  the  com- 
binations of  the  actions  are  altered,  and  the  intricacies  of 
their  co-operations  enhanced. 


CHAPTER  X. 

INTERNAL    FACTORS. 

§  153.  We  saw  at  the  outset  (§§  10—16),  that  organic 
matter  is  built  up  of  molecules  so  extremely  unstable,  that 
the  slightest  variation  in  their  conditions  destroys  their 
equilibrium ;  and  causes  them  either  to  assume  altered 
structures  or  to  decompose.  But  a  substance  which  is  beyond 
all  others  changeable  by  the  actions  and  reactions  of  the 
forces  liberated  from  instant  to  instant  within  its  own 
mass,  must  be  a  substance  that  is  beyond  all  others  change- 
able by  the  forces  acting  on  it  from  without.  If  their 
composition  fits  organic  aggregates  for  undergoing  with 
special  facility  and  rapidity  those  re-distributions  of  matter 
and  motion  whence  result  individual  organization  and  life : 
then  their  composition  must  make  them  similarly  apt  to 
imdergo  those  permanent  re-distributions  of  matter  and  mo- 
tion which  are  expressed  by  changes  of  structure,  in  corre- 
spondence with  permanent  re-distributions  of  matter  and 
motion  in  their  environments. 

Already  in  First  Principles,  when  considering  the  phe- 
nomena of  Evolution  in  general,  the  leading  characters  and 
causes  of  those  changes  which  constitute  organic  evolution, 
were  briefly  traced.  Under  each  of  the  derivative  laws  of 
force  to  which  the  passage  from  an  incoherent,  indefinite 
homogeneity  to  a  coherent,  definite  heterogeneity,  conforms, 
were  given  illustrations  drawn  from  the  metamorphoses  ot 


INTERNAL   FACTORS.  421 

living  bodies.  Here  it  will  be  needful  to  contemplate  tho 
several  resulting  processes  as  going  on  at  once,  in  both 
individuals  and  species. 

§  154.  Our  postulate  being  tbat  organic  evolution  in  ge- 
neral commenced  with  homogeneous  organic  matter,  just  as 
the  evolution  of  individual  organisms  commences,  we  have 
first  to  remember  that  the  state  of  homogeneity  is  an  un- 
stable state  (First  Principle?,  §  109).  In  any  aggregate 
"the  relations  of  outside  and  inside,  and  of  comparative 
nearness  to  neighbouring  sources  of  influence,  imply  the  re- 
ception of  influences  that  are  unlike  in  quantity  or  quality, 
or  both ;  and  it  follows  that  \mlike  changes  will  be  produced 
in  the  parts  thus  dissimilarly  acted  upon."  Further,  "  if 
any  given  whole,  instead  of  being  absolutely  uniform  through- 
out, consists  of  parts  distinguishable  from  each  other — if 
each  of  these  parts,  while  somewhat  unlike  other  parts,  is 
uniform  within  itself;  then,  each  of  them  being  in  unstable 
equilibrium,  it  follows  that  while  the  changes  set  up  within 
it  must  render  it  multiform,  they  must  at  the  same  time 
render  the  whole  more  multiform  than  before ;  "  and  hence, 
"  whether  that  state  with  which  we  commence  be  or  be  not 
une  of  perfect  homogeneity,  the  process  must  equally  be 
towards  a  relative  heterogeneity."  This   loss   of 

homogeneity  which  the  special  instability  of  organic  aggre- 
gates fits  them  to  display  more  promptly  and  variously  than 
any  other  aggregates,  must  be  shown  in  more  numerous 
ways  in  proportion  as  the  incident  forces  are  more  numerous. 
Every  differentiation  of  structure  being  a  result  of  some 
difference  in  the  relations  of  the  parts  to  the  agencies  acting 
on  them,  it  follows  that  the  more  multiplied  and  more  unlike 
the  agencies,  the  more  varied  must  be  the  differentiations 
wrought.  Hence  the  gravitation  from  a  state  of  homogeneity 
to  a  state  of  heterogeneity,  will  be  conspicuously  shown  in 
proportion  as  the  environment   is  complex.  This 

'ransition  from  a  uniform  to  a  multiform  state,  must  con- 


422  THE   EVOLUTION    OF   LIFE. 

tinue  through  successive  individuals.  Given  a  series  of  or- 
ganisms, each  of  which  is  developed  from  a  portion  of  a 
preceding  organism,  and  the  question  is,  whether,  after 
exposure  of  the  series  for  a  million  years  to  changed  incident 
forces,  one  of  its  members  will  be  the  same  as  though  the 
incident  forces  had  only  just  changed.  To  say  that  it  will, 
is  implicitly  to  deny  the  persistence  of  force.  In  relation  to 
any  cause  of  divergence,  the  whole  series  of  such  organisms 
may  be  considered  as  fused  together  into  a  continuously- 
existing  organism ;  and  when  so  considered,  it  becomes 
manifest  that  a  continuously-acting  cause  will  go  on  working 
a  continuously-increasing  effect,  until  some  counteracting 
cause  prevents  any  further  effect. 

But  now  if  any  primordial  organic  aggregate,  must,  in  itself 
and  through  its  descendants,  gravitate  from  uniformity  to 
multiformity,  in  obedience  to  the  more  or  less  multiform 
forces  acting  on  it ;  what  must  happen  if  these  multiform 
forces  are  themselves  ever  undergoing  slow  variations  and 
complications  ?  Clearly  the  process,  ever- advancing  towards 
a  temporary  limit  but  ever  having  its  limit  removed,  must 
go  on  unceasingly.  On  those  structural  changes  wrought 
in  the  once  homogeneous  aggregate  by  an  original  set  of  in- 
cident forces,  will  be  superposed  further  changes  wrought 
by  a  modified  set  of  incident  forces ;  and  so  on  throughout 
all  time.  Omitting  for  the  present  those  circumstances 
which  check  and  qualify  its  consequences,  the  instability  of 
the  homogeneous  must  be  recognized  an  ever-acting  cause  of 
organic  evolution,  as  of  all  other  evolution. 

"While  it  follows  that  every  organism,  considered  as  an  in- 
dividual and  as  one  of  a  series,  tends  thus  to  pass  into  a  more 
heterogeneous  state ;  it  also  follows  that  every  species,  con- 
sidered as  an  aggregate  of  individuals,  tends  to  do  the  like. 
Throughout  the  area  it  inhabits,  the  conditions  can  never 
be  absolutely  uniform :  its  members  must,  in  different  parts 
of  its  area,  be  exposed  to  different  sets  of  incident  forces. 
Still  more  decided  must  this  difference  of  exposure  be  when 


INTERNAL   FACTORS.  423 

its  members  spread  into  other  habitats.  Those  expansive 
and  repressive  energies  which  set  to  each  species  a  limit  that 
perpetually  oscillates  from  side  to  side  of  a  certain  mean,  are, 
as  we  lately  saw,  frequently  changed  by  new  combinations 
of  the  external  factors — astronomic,  geologic,  meteorologic, 
and  organic.  Hence  there  from  time  to  time  arise  lines  of  di- 
minished resistance,  along  which  the  species  flows  into  new 
localities.  Such  portions  of  the  species  as  thus  migrate,  are 
subject  to  circumstances  markedly  contrasted  with  its  average 
circumstances.  And  from  multiformity  of  the  circumstances, 
must  come  multiformity  of  the  species. 

Thus  the  law  of  the  instability  of  the  homogeneous,  has  here 
a  three-fold  corollary.  As  interpreted  in  connexion  with  the 
ever-progressing,  ever-complicating  changes  in  external  fac- 
tors, it  brings  us  to  the  conclusion  that  there  must  be  a  pre- 
vailing tendency  towards  greater  heterogeneity  in  all  kinds 
of  organisms,  considered  both  individually  and  in  successive 
generations ;  as  well  as  in  each  assemblage  of  organisms  con- 
stituting a  species ;  and,  by  consequence,  in  each  genus, 
order,  and  class 

§  155.  When  considering  the  causes  of  evolution  in 
general,  we  further  saw  (First  Principles,  §  116),  that  the 
multiplication  of  effects  aids  continually  to  increase  that 
heterogeneity  into  which  homogeneity  inevitably  lapses.  It 
was  pointed  out  that  since  "  the  several  parts  of  an  aggre- 
gate are  differently  modified  by  any  incident  force ; "  and 
that  since  "  by  the  reactions  of  the  differently  modified  parts 
the  incident  force  itself  must  be  divided  into  differently 
modified  parts ;  "  it  follows  that  "  each  differentiated  di- 
vision of  the  aggregate  thus  becomes  a  centre  from  which 
a  differentiated  division  of  the  original  force  is  again 
diffused.  And  since  unlike  forces  must  produce  unlike 
results,  each  of  these  differentiated  forces  must  produce, 
throughout  the  aggregate,  a  further  series  of  differentia- 
tions.""    And  to  this  it  was  added,   that  in  proportion  ii£ 


424 


THE    EVOLUTION   OF    LIFE. 


the  heterogeneity  increases,  the  complications  arising  from 
this  multiplication  of  effects  grow  more  marked ;  since 
the  more  strongly  contrasted  the  parts  of  an  aggregate 
become,  the  more  different  must  be  their  reactions  upon 
incident  forces,  and  the  more  unlike  must  be  the  secondary 
sets  of  effects  which  these  modified  incident  forces  initiate ; 
and  since  every  increase  in  the  number  of  unlike  parts 
increases  the  number  of  such  differentiated  incident  forces, 
and  such  secondary  sets  of  effects. 

How  this  multiplication  of  effects  conspires  with  the  in- 
stability of  the  homogeneous,  to  work  an  increasing  multi- 
formity of  structure  in  an  organism,  was  shown  at  the  time ; 
and  the  foregoing  pages  contain  further  incidental  illustra- 
tions. Under  the  head  of  Adaptation  (§  69),  it  was  shown 
that  a  change  in  one  function  must  act  and  re-act  through 
ever-complicating  perturbations  on  the  rest;  and  that,  eventu- 
ally, all  parts  of  the  organism  must  be  modified  in  their 
states.  Suppose  that  the  head  of  a  mammal  becomes  very 
much  more  weighty — what  must  be  the  indirect  results? 
The  muscles  of  the  neck  are  put  to  greater  exertions ;  and 
its  vertebras  have  to  bear  additional  tensions  and  pressures, 
caused  both  by  the  increased  weight  of  the  head,  and  the 
stronger  contractions  of  the  muscles  that  support  and  move  the 
head.  These  muscles  also  affect  their  own  attachments :  several 
of  the  dorsal  spines  have  augmented  strains  put  on  them ; 
and  the  vertebrae  to  which  they  are  fixed,  are  more  severely 
taxed.  Further,  this  heavier  head  and  the  more  massive 
neck  it  necessitates,  require  a  stronger  fulcrum :  the  whole 
thoracic  arch,  and  the  fore  limbs  which  support  it,  are  sub- 
ject to  greater  continuous  stress  and  more  violent  occasional 
shocks.  And  the  required  strengthening  of  the  fore- quarters 
cannot  take  place,  without  the  centre  of  gravity  being 
changed,  and  the  hind  limbs  being  differently  reacted  upon 
during  locomotion.  Any  one  who  compares  the  outline 
of  the  bison  with  that  of  its  congener,  the  ox,  will  clearly 
see  how  profoundly  a  heavier  head  affects  the  entire  osseous 


INTERNAL   FACTORS.  425 

and  muscular  systems.  Besides  this  multiplica- 

tion of  mechanical  effects,  there  is  a  multiplication  of 
physiological  effects.  The  vascular  apparatus  is  modified 
throughout  its  whole  structure,  by  each  considerable  modifi- 
cation in  the  proportions  of  the  body.  Increase  in  the  size 
of  any  organ,  implies  a  quantitative,  and  uften  a  qualitative, 
reaction  on  the  blood ;  and  so  alters  the  nutrition  of  all  other 
organs.  Such  physiological  correlations  are  exemplified  in  the 
many  differences  that  accompany  difference  of  sex.  That  the 
minor  sexual  peculiarities  are  brought  about  by  the  physio- 
logical actions  and  reactions,  is  shown  both  by  the  fact  that 
they  are  commonly  but  faintly  marked  until  the  fundamentally 
distinctive  organs  are  developed ;  and  that  when  the  de- 
velopment of  these  is  prevented,  the  minor  sexual  peculiarities 
do  not  arise.  No  further  proof  is,  I  think,  needed, 

that  in  any  individual  organism  or  its  descendants,  a  new 
external  action  must,  besides  the  primary  internal  change 
which  it  works,  work  sundry  secondary  changes,  as  well  as 
tertiary  changes  still  more  multiplied.  That  tendency  to- 
wards greater  heterogeneity  which  is  given  to  an  organ- 
ism by  disturbing  its  environment,  is  helped  by  the  tendency 
which  every  modification  lias  to  produce  other  modifications 
— modifications  which  must  become  more  numerous  in  pro- 
portion as  the  organism  becomes  more  complex.  And 
then,  lastly,  among  the  indirect  and  involved  manifestations 
of  this  tendency,  we  must  not  omit  the  innumerable  small 
irregularities  of  structure  that  result  from  the  crossing  of 
dissimilarly-modified  individuals.  It  was  shown  (§§  89,  90) 
'hat  what  are  called  "spontaneous  variations,"  are  inter- 
pretable  as  results  of  miscellaneously  compounding  the 
changes  wrought  in  different  lines  of  ancestors  by  different 
conditions  of  life.  These  still  more  complex  and  multi- 
tudinous effects  so  produced,  are  thus  further  illustrations  of 
the  multiplication  of  effects. 

Equally  in  the  aggregate  of  individuals  constituting  a 
species,  does  multiplication  of  effects  become  the  continual 
28 


426  THE    EVOLUTION    OF    LIFE. 

cause  of  increasing  multiformity.  The  lapse  of  a  species  into 
divergent  varieties,  initiates  frc«h  combinations  of  forces 
tending  to  work  further  divergences.  The  new  varieties 
compete  with  the  parent  species  in  new  ways ;  and  so  add  new 
elements  to  its  circumstances.  They  modify  somewhat  the 
conditions  of  other  species  existing  in  their  habitat,  or  intc 
whose  habitat  they  have  spread;  and  the  modifications 
wrought  in  such  other  species,  become  additional  sources  of 
influence.  The  Flora  and  Fauna  of  every  region  are  united 
by  their  entangled  relations  into  a  whole,  of  which  no  part 
can  be  affected  without  affecting  the  rest.  Hence,  each  dif- 
ferentiation in  a  local  assemblage  of  species,  becomes  the 
cause  of  further  differentiations  in  such  assemblage. 

§  15G.  One  of  the  universal  principles  to  which  we  saw 
that  the  re- distribution  of  matter  and  motion  conforms,  is 
that  in  any  aggregate  made  up  of  mixed  units,  incident 
forces  produce  segregation — separate  unlike  units  and  unite 
Like  units ;  and  it  was  shown  that  the  increasing  integration 
and  definiteness  which  characterizes  each  part  of  an  evolving 
organic  aggregate,  as  of  every  other  aggregate,  results  from 
this  (First  Principles,  §  126).  It  remains  here  to  be 
pointed  out,  that  while  the  actions  and  reactions  going  on 
between  organisms  and  their  ever-changing  environments, 
add  to  the  heterogeneity  of  organic  structures,  they  also 
give  to  the  heterogeneity  this  growing  distinctness.  At 
first  sight  the  reverse  might  be  inferred.  It  might  be  argued 
that  any  new  set  of  effects  wrought  in  an  organism  by  some 
new  set  of  external  forces,  must  tend  more  or  less  to  obliter- 
ate the  effects  previously  wrought — must  produce  confusion 
or  indefiniteness.  A  little  consideration,  however,  will  dissi- 
pate this  impression. 

Doubtless  the  condition  under  which  alone  increasing  de- 
finiteness of  structure  can  be  acquired  by  any  part  of  an  or- 
ganism, either  in  an  individual  or  in  successive  generations,  is 
that  such  part  shall  be  exposed  to  some  set  of  tolerably-con- 


INTERKAL    FACTORS.  427 

elant  forces;  and  doubtless,  continual  change  of  circumstances 
interferes  with  this.  But  the  interference  can  never  be  con- 
siderable. For  the  pre-existing  structure  of  an  organism  pre- 
vents it  from  living  under  any  new  conditions  except  such  as 
are  congruous  with  the  fundamental  characters  of  its  organiza- 
tion— such  as  subject  its  essential  organs  to  actions  substan- 
tially the  same  as  before.  Great  changes  must  kill  it.  Hence, 
it  can  continuously  expose  itself  and  its  descendants,  only  to 
those  moderate  changes  which  do  not  destroy  the  general  har- 
mony between  the  aggregate  of  incident,  forces  and  the  ag- 
gregate of  its  functions.  That  is,  it  must  remain  under 
influences  calculated  to  make  greater  the  definiteness  of 
the  chief  differentiations  already  produced.  If,  for  ex- 
ample, we  set  out  with  an  animal  in  which  a  rudimentary 
vertebral  column  with  its  attached  muscular  system  has 
been  established ;  it  is  clear  that  the  mechanical  arrange- 
ments have  become  thereby  so  far  determined,  that  sub- 
sequent modifications  are  extremely  likely,  if  not  certain,  to 
be  consistent  with  the  production  of  movement  by  the  action 
of  muscles  on  a  flexible  central  axis.  Hence,  there  will  con- 
tinue a  general  similarity  in  the  play  of  forces  to  which  tho 
flexible  central  axis  is  subject ;  and  so,  notwithstanding  the 
metamorphoses  which  the  vertebrate  type  undergoes,  there 
will  be  a  maintenance  of  conditions  favourable  to  increasing 
definiteness  and  integration  of  the  vertebral  column.  More- 
over, this  maintenance  of  such  conditions  becomes  secure  in 
proportion  as  organization  advances.  Each  further  com- 
plexity of  structure,  implying  some  further  complexity  in 
the  relations  between  an  organism  and  its  environment,  must 
tend  to  specialize  the  actions  and  reactions  between  it  and  its 
environment — must  tend  to  increase  the  stringency  with 
which  it  is  restrained  within  such  environments  as  admit  of 
those  special  actions  and  reactions  for  which  its  structure  fits 
it ;  that  is,  must  further  guarantee  the  continuance  of  those 
actions  and  reactions  to  which  its  essential  organs  respond, 
and  therefore  the  continuance  of  the  segregating  process. 


428  THE   EVOLUTION   OF    LIFE. 

How  in  each  species,  considered  as  an  aggregate  of  indi- 
viduals, there  must  arise  stronger  and  stronger  contrasts 
between  those  divergent  varieties  which  result  from  the 
instability  of  the  homogeneous  and  the  multiplication  of 
effects,  needs  only  oe  briefly  indicated.  It  has  already 
been  shown  (First  Principles,  §  126),  that  in  conformity  to 
the  universal  law  that  mixed  units  are  segregated  by  like 
incident  forces,  there  are  produced  increasingly-definite 
distinctions  among  varieties,  wherever  there  occur  definitely- 
distinguished  sets  of  conditions  to  which  the  varieties  are  re- 
spectively subject. 

§  157.  Probably  in  the  minds  of  some,  the  reading  of  this 
chapter  has  been  accompanied  by  a  running  commentary,  to 
the  effect  that  the  argument  proves  too  much.  The  apparent 
implication  is,  that  the  passage  from  an  indefinite,  incohe- 
rent homogeneity  to  a  definite,  coherent  heterogeneity  in 
organic  aggregates,  must  have  been  going  on  universally ; 
whereas  we  find  that  in  many  cases  there  has  been  persist- 
ence without  progression.  This  apparent  implication,  how- 
aver,  is  not  a  real  one. 

For  though  every  environment  on  the  Earth's  surface 
undergoes  changes ;  and  though  usually  the  organisms 
which  each  environment  contains,  cannot  escape  certain 
resulting  new  influences ;  yet  occasionally  such  new  in- 
fluences are  escaped,  by  the  survival  of  species  in  the  un- 
changed parts  of  their  habitats,  or  by  their  spread  -into 
neighbouring  habitats  which  the  change  has  rendered  like 
their  original  habitats,  or  by  both.  Any  alteration  in  the 
temperature  of  a  climate  or  its  degree  of  humidity,  is  Jn- 
likely  to  affect  simultaneously  the  whole  area  occupied  by  a 
species;  and  further,  it  can  scarcely  fail  to  happen  that  the 
addition  or  subtraction  of  heat  or  moisture,  will  give  to  a 
part  of  some  adjacent  area,  a  climate  like  to  that  to  which 
the  species  lias  been  habituated.  If,  again,  the  circumstances 
of  a  species  are  modified  by  the  intrusion  of  some  foreign 


INTERNAL    FACTORS.  429 

kind  of  plant  or  animal,  it  follows  that  since  the  intruders 
will  probably  not  spread  throughout  its  whole  habitat,  the 
species  will,  in  one  or  more  localities,  remain  unaffected  by 
them.  Especially  among  marine  creatures,  must  there  fre- 
quently occur  cases  in  which  modifying  causes  are  con- 
tinually eluded.  Much  more  uniform  as  are  the  physical 
conditions  to  which  the  sea  exposes  its  inhabitants,  it  becomes 
possible  for  such  of  them  as  live  on  widely-diffused  food,  to 
be  widely  distributed;  and  wide  distribution  generally  pre- 
vents the  members  of  a  species  from  being  all  subject  to  the 
same  cause.  Our  commonest  cirrhiped,  for  instance,  subsisting 
on  minute  creatures  that  are  everywhere  dispersed  through 
the  sea ;  needing  only  to  have  some  firm  surface  on  which 
to  build  up  its  shell ;  and  in  scarcely  any  danger  from  sur- 
rounding animals;  is  able  to  exist  on  shores  so  widely  remote 
from  one  another,  that  nearly  every  change  in  the  actions  of 
incident  forces,  must  fall  within  narrower  areas  than  that 
which  the  species  occupies.  In  nearly  every  case,  therefore, 
a  portion  of  the  species  will  survive  unmodified.  Its  easily- 
transported  germs  will  take  possession  of  such  new  habitats 
as  have  been  rendered  fitter  by  the  change  that  has  unfitted 
some  parts  of  its  original  habitat.  Hence,  on  successive 
occasions,  while  some  parts  of  the  species  are  slightly  trans- 
formed, another  part  may  continually  escape  transformation 
by  migrating  hither  and  thither,  where  the  simple  condi- 
tions needed  for  its  existence  recur  in  nearly  the  same  com- 
binations as  before.  And  it  will  so  become  possible  for  it 
to  survive,  with  comparatively  trifling  structural  changes, 
throughout  long  geologic  periods. 

§  158.  The  results  to  which  we  find  ourselves  led,  aro 
thes3. 

In  subordination  to  the  different  amounts  and  kinds  of 
forces  to  which  its  different  parts  are  exposed,  every  in- 
dividual organic  aggregate,  like  all  other  aggregates,  tends 
to  pass  from  its  original  indistinct  simplicity  towards  a  more 


430  THE    EVOLUTION   OF    LTPE. 

distinct  complexity.  Unless  we  deny  the  persistence  of 
force,  we  must  admit  that  the  gravitation  of  an  organisn.-'s 
structure  from  an  indefinitely  homogeneous  to  a  definitely 
heterogeneous  state,  must  be  cumulative  in  successive  genera- 
tions, if  the  forces  causing  it  continue  to  act.  And  for  the 
like  reasons,  the  increasing  assemblage  of  individuals  arising 
from  a  common  stock,  is  also  liable  to  lose  its  original 
uniformity ;  and,  in  successive  generations,  to  grow  more 
pronounced  in  its  multiformity. 

These  changes,  which  would  go  on  to  but  a  comparatively 
small  extent  were  organisms  exposed  to  constant  external 
conditions,  are  kept  up  by  the  continual  changes  in  external 
conditions,  produced  by  astronomic,  geologic,  meteorologic, 
and  organic  agencies :  the  average  result  being,  that  on 
previous  complications  of  structure  wrought  by  previous 
incident  forces,  new  complications  are  continually  superposed 
by  new  incident  forces.  And  hence  simultaneously  arises 
increasing  heterogeneity  in  the  structures  of  individuals,  in 
the  structures  of  species,  and  in  the  structures  of  the  Earth's 
Flora  and  Fauna. 

But  while,  in  very  many  or  in  most  cases,  the  ever- 
changing  incidence  of  forces  is  ever  adding  to  the  complexity 
of  organisms,  and  to  the  complexity  of  the  organic  world  as  a 
whole ;  it  does  this  only  where  its  action  cannot  be  eluded. 
And  since,  hy  migration,  it  is  possible  for  species  to  keep 
themselves  under  conditions  that  are  tolerably  constant ; 
there  must  be  a  proportion  of  cases  in  which  greater  hetero- 
geneity of  structure  is  not  produced. 

Uniting  these  three  propositions,  we  are  brought  to  a  eon 
elusion  which,  so  far  as  it  goes,  appears  to  be  in  harnior.y 
with  the  facts.  We  find  progression  to  result,  not  from  a 
special,  inherent  tendency  of  living  bodies,  but  from  a  general 
average  effect  of.  their  relations  to  surrounding  agencies. 
While  we  are  not  called  on  to  suppose  that  there  exists  in 
organisms  any  primordial  impulse  which  makes  them  con- 
tinually  unfold   into    more   heterogeneous   forms;    -we   see 


INTERNAL    FACTORS.  431 

that  a  liability  to  be  unfolded  arises  from  the  actions  and 
reactions  between  organisms  and  their  fluctuating  environ- 
ments. And  we  see  that  the  existence  of  such  a  cause  of 
development,  presupposes  the  non-occurrence  of  development 
where  this  fluctuation  of  actions  and  reactions  does  not 
come  into  play. 

To  show,  however,  that  there  must  arise  a  certain  general 
tendency  to  the  production  of  more  heterogeneous  aggregates, 
is  not  sufficient.  It  is  quite  conceivable  that  aggregates 
should  be  rendered  more  heterogeneous  by  changing  incident 
forces,  without  having  given  to  them  that  peculiar  form  of 
heterogeneity  required  for  carrying  on  the  functions  of  life. 
Hence  it  remains  now  to  inquire,  how  the  production  and 
maintenance  of  this  peculiar  form  of  heterogeneity  is  insured. 


CHAPTER   XL 

DIRECT   EQUILIBRATION. 

§  159.  Every  change  is  of  necessity  towards  a  balance  of 
loi  ces ;  ana  of  necessity  can  never  cease  until  a  Dalance  ot  lorces 
is  reached.  When  treating  of  equilibration  under  its  general 
aspects  (First  Principles,  Part  II.,  Chap,  xvi.),  we  saw  that 
in  every  aggregate  having  compound  movements,  there 
tends  continually  to  be  established  a  moving  equilibrium ; 
since  any  unequilibrated  force  to  which  such  an  aggregate 
is  subject,  if  not  of  a  kind  to  overthrow  the  aggregate  al- 
together, must  continue  modifying  its  state  until  an  equi- 
librium is  brought  about.  And  we  saw  that  the  structure 
simultaneously  reached  must  be  "  one  presenting  an  arrange- 
ment of  forces  that  counterbalance  all  the  forces  to  which  the 
aggregate  is  subject ; "  since,  "  so  long  as  there  remains  a 
residual  force  in  any  direction — be  it  excess  of  a  force 
exercised  by  the  aggregate  on  its  environment,  or  of  a  force 
exercised  by  its  environment  on  the  aggregate,  equilibrium 
does  not  exist ;  and  therefore  the  re-distribution  of  matter 
must  continue." 

It  is  essential  that  this  truth  should  here  be  fully  under- 
stood ;  and  to  the  end  of  insuring  a  clear  comprehension  of 
it,  some  re-illustration  is  desirable.  The  case  of  the  Solar 
System  will  best  serve  our  purpose.  An  assemblage  of  bodies, 
each  of  which  has  its  simple  and  compound  motions,  that 
severally  alternate  between  two  extremes,  and  the  whole  of 


DIEECT    EQUILIBRATION.  433 

which  has  its  involved  perturbations,  that  now  increase  and 
now  decrease,  is  heie  presented  to  us.  Suppose  a  new 
force  were  brought  to  bear  on  this  moving  equilibrium — say 
by  the  arrival  of  some  wandering  mass,  or  by  an  additional 
momentum  given  to  one  of  the  existing  masses — what  would 
be  the  result  ?  If  the  strange  body  or  the  extra  force  were 
very  large,  it  might  so  derange  the  entire  system  as  to  cause 
its  collapse :  by  overthrow  of  its  rhythmical  movements,  the 
moving  equilibrium  might  rapidly  be  changed  into  a  com- 
plete equilibrium.  But  what  if  the  incident  force,  falling  on 
the  system  from  without,  proved  insufficient  to  overthrow  it? 
There  would  then  arise  a  set  of  perturbations  which  would, 
in  the  course  of  an  enormous  period,  slowly  work  round  into 
a  modified  moving  equilibrium.  The  effects  primarily  ini- 
pyessed  on  the  adjacent  masses,  and  in  a  smaller  degree  on 
the  remoter  masses,  would  soon  become  complicated  with  the 
secondary  effects  impressed  by  the  disturbed  masses  on  one 
another ;  and  these  again  with  tertiary  effects.  Waves  of 
perturbation  would  continue  to  be  propagated  throughout 
the  entire  system ;  until,  around  a  new  centre  of  gravity, 
there  had  been  established  a  set  of  planetary  motions  more 
or  less  different  from  the  preceding  ones.  All  this  would 
necessarily  follow  from  the  truth,  that  any  new  force  brought 
to  bear  on  a  moving  equilibrium,  must  gradually  be  used  up 
in  overcoming  the  forces  that  resist  the  divergence  it  gener- 
ates :  which  antagonizing  forces,  being  then  no  longer  op- 
posed, set  up  i  counter-action,  ending  in  a  compensating 
divergence  in  the  opposite  direction,  that  is  followed  by  a 
re-compensating  divergence ;  and  so  on,  until  there  is  either 
established  some  additional  rhythmical  movement,  or  some 
equivalent  modification  of  the  pre-existing  rhythmical  move- 
ments. Now  though  instead  of  being,  like  the  Solar 
System,  in  a  state  of  independent  moving  equilibrium,  an 
organism  is  in  a  state  of  dependent  moving  equilibrium 
(First  Principles,  §  130) ;  yet  this  does  not  prevent  the 
manifestation  of  the  same  law.     Every  animal  daily  obtains 


434  THE    EVOLUTION    OF    LIFE. 

from  without,  a  supply  of  force  to  replace  the  force 
which  it  expends ;  but  this  continual  giving  to  its  parts  a 
new  momentum,  to  make  up  for  the  momentum  continually 
lost,  does  not  interfere  with  the  carrying  on  of  actions  and 
reactions  like  those  just  described.  Here,  as  before,  we  have 
a  definitely-arranged  aggregate  of  parts,  which  we  call 
organs,  having  their  definitely-established  actions  and  re- 
actions, which  we  call  functions.  These  rhythmical  actions 
or  functions,  and  the  various  compound  rhythms  resulting 
from  their  combinations,  are  in  such  adjustment  as  to  balance 
the  actions  to  which  the  organism  is  subject :  there  is  a  con- 
stant or  periodic  genesis  of  forces,  which,  in  their  kinds, 
amounts,  and  directions,  suffice  to  antagonize  the  forces 
which  the  organism  has  constantly  or  periodically  to  bear. 
If  then  there  exists  this  state  of  moving  equilibrium  among 
a  definite  set  of  internal  actions,  exposed  to  a  definite  set  of  ex- 
ternal actions ;  what  must  result  if  any  of  the  external  actions 
are  changed  ?  Of  course  there  is  no  longer  an  equilibrium. 
Some  force  which  the  organism  habitually  generates,  is  too 
great  or  too  small  to  balance  some  incident  force ;  and  there 
arises  a  residuary  force  exerted  by  the  environment  on  the 
organism,  or  by  the  organism  on  the  environment.  This 
residuary  force — this  unbalanced  force,  of  necessity  expends 
itself  in  producing  some  change  of  state  in  the  organism. 
Acting  directly  on  some  organ  and  modifying  its  function, 
it  indirectly  modifies  dependent  functions,  and  remotely 
influences  all  the  functions.  As  we  have  already  seen 
(§§  68,  69),  if  this  new  force  is  permanent,  its  effects  must 
be  gradually  diffused  throughout  the  entire  system ;  until  it 
has  come  to  be  equilibrated  in  working  those  structural  re- 
arrangements which  produce  an  exactly  counterbalancing 
force. 

The  bearing  of  this  general  truth  on  the  question  we  are 
now  dealing  with,  is  obvious.  Those  modifications  upon 
modifications,  which  the  unceasing  mutations  of  their  en- 
vironments have  been  all  along  generating  in   organisms, 


DIRECT    EQUILIBRATION.  435 

have  been  in  each  case  modifications  involved  by  the 
establishment  of  a  new  balance  with  the  new  combination  of 
conditions.  In  every  species  throughout  all  geologic  time, 
there  has  been  perpetually  going  on  a  rectification  of  the 
equilibrium,  that  has  been  perpetually  disturbed  by  the 
alteration  of  surrounding  circumstances  ;  and  every  further 
heterogeneity  has  been  the  addition  of  a  structural  change 
entailed  by  a  new  equilibration,  to  the  structural  changes 
entailed  by  previous  equilibrations.  There  can  be  no  other 
ultimate  interpretation  of  the  matter,  since  change  can  have 
no  other  goal.  Any  fresh  force  brought  to  bear  on  an 
aggregate  in  a  state  of  moving  equilibrium,  must  do  one  of 
two  things :  it  must  either  overthrow  the  moving  equi- 
librium altogether,  or  it  must  alter  without  overthrowing  it ; 
and  the  alteration  must  end  in  the  establishment  of  a  new 
moving  equilibrium.  Hence  in  organisms,  death  or  restora- 
tion of  the  physiological  balance,  are  the  only  alternatives. 

This  equilibration  between  the  functions  of  an  organism 
find  the  actions  in  its  environment,  may  be  either  direct  or 
indirect.  The  new  incident  force  may  either  immediately 
call  forth  some  counteracting  force,  and  its  concomitant 
structural  change ;  or  it  may  be  eventually  balanced  by  some 
otherwise-produced  change  of  function  and  structure. 
These  two  processes  of  equilibration  are  quite  distinct,  and 
must  be  separately  dealt  with.  We  will  devote  this  chapter 
to  the  first  of  them. 

§  160.  Direct  equilibration  is  that  process  currently 
known  as  adaptation.  We  have  already  seen  (Part  II., 
Chap,  v.),  that  individual  organisms  become  modified  when 
placed  in  new  conditions  of  life — so  modified  as  to  re-adjust 
the  powers  to  the  requirements  ;  and  though  there  is  great 
difficulty  in  disentangling  the  evidence,  we  found  reason  for 
thinking  (§  82)  that  structural  changes  thus  caused  by 
functional  changes  are  inherited.  In  the  last  chapter,  it 
v/as  argued  that  if,  instead  of  the  succession  of  individuals 


436  THE    EVOLUTION   01'   LIFE. 

constituting  a  species,  there  were  a  continuously-existing 
individual,  any  such  functional  and  structural  divergence  as 
we  see  produced  by  a  new  incident  force,  would  necessarily 
go  on  increasing  until  the  new  incident  force  was  counter- 
poised ;  and  that  the  replacing  of  a  continuously- existing 
individual  by  a  succession  of  individuals,  each  formed  out,  of 
the  mod  ified  substance  of  its  predecessor,  will  not  prevent  the 
like  effect  from  being  produced — the  persistence  of  force 
negativing  any  other  inference.  Here  we  further  find,  that 
this  limit  towards  which  any  such  organic  change  advances, 
in  the  species  as  in  the  individual,  is  a  new  moving  equi- 
librium adjusted  to  the  new  arrangement  of  external  forces. 

But  now,  what  are  the  conditions  under  which  alone,  direct 
equilibration  can  occur  ?  Are  all  the  modifications  that  serve 
to  re-fit  organisms  to  their  environments,  directly  adaptive 
modifications?  And  if  otherwise,  which  are  the  directly 
adaptive  and  which  are  not  ?  How  are  we  to  distinguish 
between  them  ? 

Manifestly,  for  any  moving  equilibrium  to  be  gradually 
altered,  it  is  needful,  first,  that  some  force  shall  operate  upon . 
it ;  and,  second,  that  the  force  shall  not  be  such  as  to  over- 
throw it.  If  in  the  environment  there  exists  some  agency 
that  would  act  advantageously  on  an  organism  were  the  or- 
ganism a  little  modified,  but  which  does  not  act  on  it  in  the 
absence  of  the  required  modification ;  it  is  clear  that  this 
agency  cannot  itself  tend  to  produce  the  modification.  On 
the  other  hand,  if  the  external  agency  be  of  such  kind,  that 
individuals  of  the  species  whenever  affected  by  it,  are  either 
killed  or  so  injured  that  the  production  of  vigorous  offspring 
is  much  interfered  with,  there  cannot  be  directly  wrought  in 
tho  species,  any  such  alteration  as  will  fit  it  to  cope  with 
this  external  agency.  The  only  new  incident  forces  which 
can  work  the  changes  of  function  and  structure  required  to 
bring  any  animal  or  plant  into  equilibrium  with  them,  are 
such  incident  forces  as  operate  on  this  animal  or  plant, 
either  continuously  or  frequently.     They  must  be  capable 


•DIRECT   EQUILIBRATION.  437 

of  appreciably  changing  that  set  o**  complex  rhythmical 
actions  and  reactions  constituting  the  life  of  the  organism ; 
and  yet  must  not  usually  produce  perturbations  that  are 
fatal.  Let  us  see  what  are  the  limits  to  direct  equilibra- 
tion hence  arising. 

§  161.  In  plants,  organs  engaged  in  nutrition,  and  exposed 
to  variations  in  the  amounts  and  proportions  of  matters  and 
forces  utilized  in  nutrition,  may  be  expected  to  undergo  cor- 
responding variations.  We  find  evidence  that  they  do  this. 
The  "changes  of  habit "  which  are  common  in  plants,  when 
taken  to  places  unlike  in  climate  or  soil  to  those  before  in- 
habited by  them,  are  changes  of  parts  in  which  the  modified 
external  actions  directly  produce  modified  internal  actions. 
The  characters  of  the  stem  and  shoots  as  woody  or  succulent, 
erect  or  procumbent ;  of  the  leaves  in  respect  of  their  sizes, 
thicknesses,  and  textures ;  of  the  roots  in  their  degrees  of 
development  and  modes  of  growth  ;  are  obviously  in  imme- 
diate relation  to  the  characters  of  the  environment.  A  per- 
manent difference  in  the  quantity  of  light  or  heat,  affects,  day 
after  day,  the  processes  going  on  in  the  leaves.  Habitual 
rain  or  drought,  alters  all  the  assimilative  actions,  and 
appreciably  influences  the  organs  that  carry  them  on.  Some 
particidar  substance,  by  its  presence  in  the  soil,  gives  new 
qualities  to  some  of  the  tissues  ;  causing  greater  rigidity  or 
flexibility,  and  so  affecting  the  general  aspect.  Here,  then, 
we  have,  in  plants,  changes  tending  to  bring  about  in  them, 
modified  arrangements  of  functions  and  structures,  in  equi- 
librium with  modified  sets  of  external  forces. 

But  now  let  us  turn  to  other  classes  of  organs  possessed  by 
plants — organs  which  are  not  at  once  attected  in  their  actions 
by  the  variations  of  incident  forces.  Take  first  the  organs 
of  defence.  Many  plants  are  shielded  against  animals  that 
would  else  devour  them,  by  formidable  thorns ;  and  others, 
like  the  nettle,  by  stinging  hairs.  These  must  be  counted 
among  the   appliances  by  which  equilibrium  is  maintained 


438  THE    EVOLUTION   OF    LIFE. 

between  the  actions  in  the  organism  and  the  actions  in  ita 
environment ;  seeing  that  all  other  things  remaining  the 
same,  if  these  defences  were  absent,  the  destruction  by  herb- 
ivorous animals  would  be  so  increased,  that  the  number  of 
young  plants  annually  produced  would  not  suffice,  as  it  now 
does,  to  balance  the  mortality,  and  the  species  would  there- 
fore disappear.  But  these  defensive  appliances,  though  they 
aid  in  maintaining  the  balance  between  inner  and  outer 
actions,  cannot  have  been  directly  called  forth  by  the  outer 
actions  which  they  serve  to  neutralize;  for  these  outer 
actions  do  not  continuously  affect  the  functions  of  the  plant 
even  in  a  general  way,  still  less  in  the  special  Way  required. 
Suppose  a  species  of  nettle  bare  of  poison-hairs,  to  be  habit- 
ually eaten  by  some  mammal  intruding  on  its  habitat ;  the 
agency  of  this  mammal  would  have  no  direct  tendency  to 
develop  poison-hairs  in  the  plant ;  since  the  individuals 
devoured  could  not  bequeath  changes  of  structure,  even  were 
the  actions  of  a  kind  to  produce  them ;  and  since  the  in- 
dividuals that  perpetuated  themselves,  would  be  those  on 
which  the  new  incident  force  had  not  fallen.  An- 

other class  of  organs  similarly  circumstanced,  are  those  of 
reproduction.  Like  the  organs  of  defence,  these  are  not, 
during  the  life  of  the  individual  plant,  variably  exercised  by 
variable  external  actions ;  and  therefore  do  not  fulfil  those 
conditions  under  which  structural  changes  may  be  directly 
caused  by  changes  in  the  environment.  The  generative 
apparatus  contained  in  every  flower,  acts  only  once  during 
its  existence ;  and  even  then,  the  parts  subserve  their  ends 
in  a  passive  rather  than  an  active  way.  Functionally-pro- 
duced modifications  are  therefore  out  of  the  question.  If  a 
plant's  anthers  are  so  placed,  that  the  insect  which  most 
commonly  frequents  its  flowers,  is  sure  to  come  in  contact 
with  the  pollen,  and  to  fertilize  with  it  other  flowers  of  the 
same  species ;  and  if  this  insect,  dwindling  away  or  dis- 
appearing from  the  locality,  leaves  behind  no  insects  that 
have  such  shapes  aud  habits  as  cause  them  to  do  the  same 


DIRECT   EQUILIBRATION.  439 

thing  efficiently,  but  only  some  which  do  it  inefficiently ;  it 
is  clear  that  the  change  of  its  conditions,  has  no  ininiediate 
tendency  to  work  in  the  plant  any  such  structural  change 
as  shall  bring  about  a  new  balance  with  its  conditions.  For 
the  anthers,  which,  even  when  they  discharge  their  functions, 
do  it  simply  by  standing  in  the  way  of  the  insect,  are,  under 
the  supposed  circumstances,  left  untouched  by  the  insect ; 
and  this  remaining  untouched,  cannot  have  the  effect  of  so 
modifying  the  stamens  as  to  bring  the  anthers  into  a  position 
to  be  touched  by  some  other  insect.  Only  those  individuals 
whose  parts  of  fructification  so  far  differed  from  the  average 
form  of  the  species,  that  some  other  insect  could  serve  them 
as  pollen-carrier,  would  be  sufficiently  prolific  to  have  good 
chances  of  perpetuating  themselves.  And  on  their  progeny, 
inheriting  the  deviation,  there  would  act  no  external  force 
directly  calculated  to  make  the  deviation  greater,  and  the 
adaptation  more  complete ;  since  the  new  circumstances  to 
which  re-adaptation  is  required,  are  such  as  do  not  in  the 
least  alter  the  equilibrium  of  functions  constituting  the  life 
of  the  individual  plant.* 

§  162.  Among  animals,  adaptation  by  direct  equilibration 
is  similarly  traceable,  wherever,  during  the  life  of  the  indi- 
vidual, an  external  change  generates  some  constant  or  re- 
peated change  of  function.  This  is  conspicuously  the  case 
with  such  parts  of  an  animal  as  are  immediately  exposed  to 
diffused  influences,  like  those  of  climate,  and  with  such  parts 
of  an  animal  as  are  occupied  in  its  mechanical  actions  on  the 
environment.  Of  the  one  class  of  cases,  the  darkening  or 
lightening  of  the  skin,  that  follows  exposure  to  greater  or 
less  heat,  may  be  taken  as  an  instance ;  and  with  the  otber 
class  of  cases,  we  are  made  familiar  by  the  increase  and  de- 
crease which  use  and  disuse  cause  in  the  organs  of  motion 
and  manipulation.  It  is  needless  here  to  exemplify  these : 
they  were  treated  of  in  the  Second  Part  of  this  work. 

But  in  animals,  as  in  plants,  there  are  many  indispensable 


44:0  THE    EVOLUTION    OF   LIFE. 

offices  fulfilled,  by  parts,  between  which  and  the  external  con  ■ 
ditions  they  respond  to,  there  is  no  such  action  and  reaction 
as  can  directly  produce  an  equilibrium.  This  is  especially 
manifest  with  dermal  appendages.  Some  ground,  perhaps, 
exists  for  the  conclusion  that  the  greater  or  less  development 
of  hairs,  is  in  part  immediately  due  to  increase  or  decrease  of 
demand  on  their  passive  function,  as  non-conductors  of  heat ; 
but  be  this  as  it  may,  it  is  impossible  that  there  can  exist 
any  such  cause  for  those  immense  developments  of  hairs  which 
we  see  in  the  quills  of  the  porcupine,  or  those  complex  de- 
velopments of  them  known  as  feathers.  Such  an  enamelled 
armour  as  is  worn  by  the  Lepidosteus,  is  inexplicable  as  a  direct 
result  of  any  functionally- worked  change.  For  purposes  of 
defence,  such  an  armour  is  as  needful,  or  more  needful,  for 
hosts  of  other  fishes ;  and  did  it  result  from  any  direct  re- 
action of  the  organism  against  any  offensive  actions  it  was 
subject  to,  there  seems  no  reason  why  other  fishes  should  not 
have   developed    similar   protective   coverings.  Of 

sundry  reproductive  appliances,  the  like  may  be  said.  The 
secretion  of  an  egg-shell  round  the  substance  of  an  egg,  in 
the  oviduct  of  a  bird,  is  quite  inexplicable  as  a  consequence 
of  some  functionally- wrought  modification  of  structure,  im- 
mediately caused  by  some  modification  of  external  con- 
ditions. The  end  fulfilled  by  the  egg-shell,  is  that  of 
protecting  the  contained  mass  against  certain  slight  pressures 
and  collisions,  to  which  it  is  liable  during  incubation.  How, 
by  any  process  of  direct  equilibration,  could  it  come  to  have 
the  required  thickness?  or,  indeed,  how  could  it  come  to 
exist  at  all?  Suppose  this  protective  envelope  to  be  too 
weak,  so  that  some  of  the  eggs  a  bird  lays  are  broken  or 
cracked.  In  the  first  place,  the  breakages  or  crackings  are 
actions  of  a  kind  which  cannot  react  on  the  maternal  organ- 
ism, in  such  way  as  to  cause  the  secretion  of  thicker  shells 
for  the  future :  to  suppose  that  they  can,  is  to  suppose  that 
the  bird  understands  the  cause  of  the  evil,  and  that  the 
secretion  of  thicker  or  thinner  shells  can  be  controlled  by  its 


DIRECT    EQUILIBRATION.  441 

will.  In  the  second  place,  such  developing  chicks  as  are 
contained  in  the  shells  which  crack  or  break,  are  almost 
certain  to  die;  and  cannot,  therefore,  acquire  any  appro- 
priately-modified constitutions :  even  supposing  any  con- 
ceivable relation  could  be  shown,  between  the  impression 
received  and  the  change  required.  Meanwhile,  such  eggs  as 
escape  breakage,  are  not  influenced  at  all  by  the  require- 
ment ;  and  hence,  on  the  birds  developed  from  them,  there 
cannot  have  acted  any  force  tending  to  work  the  needful 
adjustment  of  functions.  In  no  way,  therefore,  can  a  direct 
equilibration  between  constitution  and  conditions  be  here 
produced.  Even  in   organs   that   can  be  modified 

by  certain  incident  forces  into  correspondence  with  such 
incident  forces,  there  are  some  re-adjustments  which  cannot 
be  effected  by  the  direct  balancing  of  inner  and  outer  actions. 
It  is  thus  with  the  bones.  The  majority  of  the  bones  have 
to  resist  muscular  strains ;  and  it  is  a  familiar  fact  that 
variations  in  the  muscular  strains,  call  forth,  by  reaction, 
variations  in  the  strengths  of  the  bones.  Here  there  is 
direct  equilibration.  But  though  the  greater  massiveness 
acquired  by  bones  subject  to  greater  strains,  may  be  ascribed 
to  a  counter-acting  force  evoked  by  a  force  brought  into 
action;  it  is  impossible  that  the  acquirement  of  greater 
lengths  by  bones  can  be  thus  accounted  for.  It  has  been 
supposed  that  the  elongation  of  the  metatarsals  in  wading 
birds,  has  resulted  from  direct  adaptation  to  conditions  of 
life.  To  justify  this  supposition,  however,  it  must  be  shown 
that  the  mechanical  actions  and  reactions  in  the  legs  of  a 
wading  bird,  differ  from  those  in  the  legs  of  other  birds  ; 
and  that  the  differential  actions  are  equilibrated  by  the  extra 
lengths.  There  is  not  the  slightest  evidence  of  thLs.  The 
metatarsals  of  a  bird,  have  to  bear  no  appreciable  strains 
but  those  due  to  the  superincumbent  weight.  Standing  in 
the  water  does  not  appreciably  alter  these  strains ;  and  even 
if  it  did,  an  increase  in  the  lengths  of  these  bones  would  not 
fit  them  any  better  to  meet  the  altered  strains. 
29 


442  THE    EVOLUTION    OF    LITE. 

§  163.  The  conclusion  at  which  we  arrive  is,  then,  that 
there  go  on  in  all  organisms,  certain  changes  of  function  and 
structure  that  are  directly  consequent  on  changes  in  the 
incident  forces — inner  changes  by  which  the  outer  changes 
are  balanced,  and  the  equilibrium  restored.  Such  re-equi- 
librations, which  are  often  conspicuously  exhibited  in  in- 
dividuals, we  have  reason  to  believe  continue  in  successive 
generations ;  until  they  are  completed  by  the  arrival  at 
structures  fitted  to  the  modified  conditions.  But,  at  the 
same  time,  we  see  that  the  modified  conditions  to  which  or- 
ganisms may  be  adapted  by  direct  equilibration,  are  con- 
ditions of  certain  classes  only.  That  a  new  external  action 
may  be  met  by  a  new  internal  action,  it  is  needful  that  i*; 
shall  either  continuously  or  frequently  be  borne  by  the  in- 
dividuals of  the  species,  without  killing  or  seriously  injuring 
them;  and  shall  act  in  such  way  as  to  affect  their  functions. 
And  we  find  on  examination,  that  many  of  the  environing 
changes  to  which  organisms  have  to  be  adjusted,  are  not  of 
these  kinds  :  being  changes  which  either  do  not  immediately 
affect  the  functions  at  all,  or  else  affect  them  in  ways  that 
prove  fatal. 

Hence  there  must  be  at  work  some  other  process,  which 
equilibrates  the  actions  of  organisms  with  the  actions  they 
are  exposed  to.  Plants  and  animals  that  continue  to  exist, 
are  necessarily  plants  and  animals  whose  powers  balance  the 
powers  that  act  on  them ;  and  as  their  environments 
change,  the  changes  which  plants  and  animals  undergo,  must 
necessarily  be  changes  towards  a  re- establishment  of  the 
balance.  Besides  direct  equilibration,  there  must  therefore 
be  an  indirect  equilibration.  How  this  goes  on  we  have  now 
to  inquire. 


CHAPTER   XIL 

INDIRECT   EQUILIBRATION. 

§  164.  Besides  those  perturbations  produced  in  the  movui£ 
equilibrium  of  any  organism  by  special  disturbing  forces, 
there  are  ever  going  on  many  other  perturbations — some 
which  are  the  still-reverberating  effects  of  disturbing  forces 
previoush*  experienced  by  the  individual,  and  others  which 
are  the  still-reverberating  effects  of  disturbing  forces  expe- 
rienced by  ancestral  individuals ;  and  the  multiplied  devia- 
tions of  function  so  caused,  imply  multiplied  deviations  of 
structure.  In  §  155  there  was  re-illustrated  the  truth,  set 
forth  at  length  when  treating  of  Adaptation  (§  69),  that  an 
organism  in  a  state  of  moving  equilibrium,  cannot  have 
extra  function  thrown  on  any  organ,  and  extra  growth  pro- 
duced in  such  organ,  without  there  being  entailed  correlative 
changes  throughout  all  other  functions,  and  eventuallv 
throughout  all  other  organs.  And  when  treating  of  Varia- 
tion (§  90),  we  saw  that  individuals  which  have  been  made, 
by  their  different  circumstances,  to  deviate  functionally  and 
structurally  from  the  average  type  in  different  directions, 
will  bequeath  to  their  joint  offspring,  compound  perturbations 
of  function  and  compound  deviations  of  structure,  endlessly 
varied  in  their  kinds  and  amounts.  That  is  to  say,  besides 
the  primary  perturbations  and  deviations  directly  caused  in 
organisms  by  altered  actions  in  their  environments,  there 
are  ever  being  indirectly  caused,  secondary  and  tertiary  per- 


444  THE    EVOLUTION    OF    LIFE. 

turbations  and  deviations,  which,  when  compounded  with  one 
another  from  generation  to  generation,  work  innumerable 
slight  modifications  in  the  moving  equilibria  and  correlative 
structures  throughout  the  species. 

Now  if  the  individuals  of  a  species  are  thus  necessarily 
made  unlike,  in  countless  ways  and  degrees — if  the  compli- 
cated sets  of  rhythms  which  we  call  their  functions,  though 
similar  in  their  general  characters,  are  dissimilar  in  their 
details — if  in  one  individual  the  amount  of  action  in  a  par- 
ticular direction  is  greater  than  in  any  other  individual,  or  if 
here  a  peculiar  combination  gives  a  resulting  force  which  is 
not  found  elsewhere ;  then,  among  all  the  individuals,  some 
will  be  less  liable  than  others  to  have  their  equilibria  over- 
thrown by  a  particular  incident  force,  previously  unexperi- 
enced. Unless  the  change  in  the  environment  is  of  so  vio- 
lent a  kind  as  to  be  universally  fatal  to  the  species,  it  must 
affect  more  or  less  differently  the  slightly  different  moving 
equilibria  which  the  members  of  the  species  present.  It 
cannot  but  happen  that  some  will  be  more  stable  than  others, 
when  exposed  to  this  new  or  altered  factor.  That  is  to  say, 
it  cannot  but  happen  that  those  individuals  whose  functions^ 
are  most  out  of  equilibrium  with  the  modified  aggregate  of 
external  forces,  will  be  those  to  die ;  and  that  those  will  sur- 
vive whose  functions  happen  to  be  most  nearly  in  equilibrium 
with  the  modified  aggregate  of  external  forces. 

But  this  survival  of  the  fittest,  implies  multiplication  of 
the  fittest.  Out  of  the  fittest  thus  multiplied,  there  will,  as 
before,  be  an  overthrowing  of  the  moving  equilibrium  wher- 
ever it  presents  the  least  opposing  force  to  the  new  incident 
force.  And  by  the  continual  destruction  of  the  individuals 
that  are  the  least  capable  of  maintaining  their  equilibria  in 
presence  of  this  new  incident  force,  there  must  eventually  be 
arrived  at  an  altered  type  completely  in  equilibrium  with  the 
altered  conditions. 

§  165.  Tins  survival  of  the  fittest,  which   I  have  hare 


INDIRECT    EQUILIBRATION.  445 

sought  to  express  in  mechanical  terms,  is  that  which  Mr  Dar- 
win has  called  "  natural  selection,  or  the  preservation  of 
favoured  races  in  the  struggle  for  life."  That  there  is  going 
on  a  process  of  this  kind  throughout  the  organic  world, 
Mr  Darwin's  great  work  on  the  Origin  of  Species  has  shown 
to  the  satisfaction  of  nearly  all  naturalists.  Indeed,  when 
once  enunciated,  the  truth  of  his  hypothesis  is  so  obvious  as 
scarcely  to  need  proof.  Though  evidence  may  be  required 
to  show  that  natural  selection  accoimts  for  everything  ascribed 
to  it,  yet  no  evidence  is  required  to  show  that  natural  selec- 
tion has  always  been  going  on,  is  going  on  now,  and  must, 
ever  continue  to  go  on.  Recognizing  this  as  an  a  priori  cer- 
tainty, let  us  contemplate  it  under  its  two  distinct  aspects. 

That  organisms  which  live,  thereby  prove  themselves  fit  to 
live,  in  so  far  as  they  have  been  tried  ;  while  organisms  which 
die,  thereby  prove  themselves  in  some  respects  unfitted  for 
living ;  are  facts  no  less  manifest,  than  is  the  fact  that  this 
self-acting  purification  of  a  species,  must  tend  ever  to  insure 
adaptation  between  it  and  its  environment.  This  adaptation 
may  be  either  so  maintained  or  so  produced.  Doubt- 

less many  who  have  looked  at  Nature  with  philosophic  eyes, 
have  observed  that  death  of  the  worst  and  multiplication  of 
the  best,  must  result  in  the  maintenance  of  a  constitution 
in  harmony  with  surrounding  circumstances.  That  the  aver- 
age vigour  of  any  race  would  be  diminished,  did  the  diseased 
and  feeble  habitually  survive  and  propagate ;  and  that  the 
destruction  of  such,  through  failure  to  fulfil  some  of  the  con- 
ditions to  life,  leaves  behind  those  which  are  able  to  fulfil  the 
conditions  to  life,  and  thus  keeps  up  the  average  fitness  to 
the  conditions  of  life  ;  are  almost  self-evident  truths.  But 
to  recognize  "  natural  selection  "  as  a  means  of  preserving 
an  already-established  balance  between  the  powers  of  a  spe- 
cies and  the  forces  to  which  it  is  subject,  is  to  recognize  it 
only  in  its  simplest  and  most  general  mode  of  action.  It  ia 
the  more  special  mode  of  action  with  which  we  are  here  con- 
cerned. This  more  special  mode  of  action,  Mr  Dar- 


446  THE   EVOLUTION    OF    LIFE. 

win  has  been  the  first  to  perceive.  To  him  we  owe  the  dis- 
covery that  natural  selection  is  capable  of  producing  fitness 
between  organisms  and  their  circumstances  ;  and  he,  too,  has 
the  merit  of  appreciating  the  immensely-important  conse- 
quences that  follow  from  this.  He  has  worked  up  an  enormous 
Diass  of  evidence  into  an  elaborate  demonstration,  that  this 
"  preservation  of  favoured  races  in  the  struggle  for  life,"  is 
an  ever-acting  cause  of  divergence  among  organic  forms. 
He  has  traced  out  the  involved  results  of  the  process  with 
marvellous  subtlety.  He  has  shown  how  hosts  of  otherwise 
inexplicable  facts,  are  fully  accounted  for  by  it.  In  brief,  he 
has  proved  that  the  cause  he  alleges  is  a  true  cause  ;  that  it 
is  a  cause  which  we  see  habitually  in  action ;  and  that  the 
results  to  be  inferred  from  it,  are  in  harmony  with  the  phe- 
nomena which  the  Organic  Creation  presents,  both  as  a  whole 
and  in  its  details.  Let  us  glance  at  a  few  of  the  more  im- 
portant interpretations  which  the  hypothesis  furnishes. 

A  soil  possessing  some  ingredient  in  unusual  quantity, 
may  supply  to  a  plant  an  excess  of  the  matter  required  for  a 
certain  class  of  its  tissues  ;  and  may  cause  all  the  parts  formed 
of  such  tissues  to  be  abnormally  developed.  Suppose  that 
among  these  are  the  hairs  clothing  its  surfaces,  including 
those  which  grow  on  its  seeds.  Thus  furnished  with  some- 
what longer  fibres,  its  seeds,  when  shed,  are  carried  a  little 
further  by  the  wind  before  they  fall  to  the  ground.  The 
young  plants  growing  up  from  them,  being  rather  more 
widely  dispersed  than  those  produced  by  other  individuals  of 
the  same  species,  will  be  less  liable  to  smother  one  another ; 
and  a  greater  number  may  therefore  reach  maturity  and 
fructify.  Supposing  the  next  generation  subject  to  the  same 
peculiarity  of  nutrition,  some  of  the  seeds  borne  by  its  mem- 
bers will  not  simply  inherit  this  increased  development  of 
hairs,  but  will  carry  it  further ;  and  these,  still  more  advan- 
taged in  the  same  way  as  before,  will,  on  the  average,  have 
still  more  numerous  chances  of  continuing  the  race.  Thus, 
by  the  survival,  generation  after  generation,  of  those  possess- 


INDIRECT    EQUILIBRATION.  447 

ing  these  longer  hairs,  and  the  inheritance  of  successive  incre- 
ments of  growth  in  the  hairs,  there  may  result  a  seed  deviat- 
ing greatly  from  the  original.  Other  individuals  of  the 
same  species,  subject  to  the  different  physical  conditions  of 
other  localities,  may  develop  somewhat  thicker  or  harder 
coatings  to  their  seeds :  so  rendering  their  seeds  less  digest- 
ible by  the  birds  that  devour  them.  Such  thicker-coated 
seeds,  by  escaping  undigested  more  frequently  than  thinner- 
coated  ones,  will  have  additional  chances  of  growing  up  and 
leaving  offspring  ;  and  this  process,  acting  in  a  cumulative 
manner  through  successive  years,  will  produce  a  seed  diverg- 
ing in  another  direction  from  the  ancestral  type.  Again, 
elsewhere,  some  modification  in  the  physiologic  actions  of 
the  plant,  may  lead  to  an  unusual  secretion  of  an  essential 
oil  in  the  seeds  ;  which  rendering  them  unpalatable  to  crea- 
tures that  would  otherwise  feed  on  them,  may  diminish  the 
destruction  of  the  seeds,  so  giving  an  advantage  to  the  variety 
in  its  rate  of  multiplication  ;  and  this  incidental  peculiarity 
proving  a  preservative,  will,  as  before,  be  gradually  increased 
by  natural  selection,  until  it  constitutes  another  divergence. 
Now  in  these  and  countless  analogous  cases,  we  see  that  plants 
may  become  better  adapted,  or  re-adapted,  to  the  aggregate  of 
surrounding  agencies,  not  through  any  direct  action  of  such 
agencies  upon  them,  but  through  their  indirect  action — 
through  the  destruction  by  them  of  the  individuals  which  are 
least  congruous  with  them,  and  the  survival  of  those  which 
are  most  congruous  with  them.  All  these  slight  variations 
of  function  and  structure,  arising  among  the  members  of  a 
species,  serve  as  so  many  experiments ;  the  great  majority  of 
which  fail,  but  a  few  of  which  succeed.  Just  as  we  see  that 
each  plant  bears  a  multitude  of  seeds,  out  of  which  some  two  or 
three  happen  to  fulfil  all  the  conditions  required  for  reaching 
maturity,  and  continuing  the  race;  so  Ave  see  that  each  species 
is  perpetually  producing  numerous  slightly-modified  forms, 
deviating  in  all  directions  from  the  average,  out  of  which 
most  fit  the  surrounding  conditions  no  better  than  their  pa- 


448  THE    EVOLUTION   OF    LIFE. 

rents,  or  not  so  well,  but  some  few  of  which  fit  the  conditio na 
better;  and  doing  so,  are  enabled  the  better  to  preserve  them- 
selves, and  to  produce  offspring  similarly  capable  of  preserv- 
ing themselves.  Among  animals  the  like  process  re- 
sults in  the  like  development  of  various  structures  which 
cannot  have  been  affected  by  the  performance  of  functions — 
their  functions  being  purely  passive.  The  thick  shell  of  u 
mollusk,  is  inexplicable  as  a  result  of  direct  reactions  of  the 
organism  against  the  external  actions  to  which  it  is  exposed ; 
but  it  is  quite  explicable  as  a  result  of  the  survival,  genera- 
tion after  generation,  of  individuals  whose  thicker  coverings 
protected  them  against  enemies.  Similarly  with  such  a 
dermal  structure  as  that  of  the  tortoise.  Though  we  have  evi- 
dence that  the  skin  where  it  is  continually  exposed  to  pres- 
sure and  friction  may  thicken,  and  so  re-establish  the  equi- 
librium, by  opposing  a  greater  inner  force  to  a  greater  outer 
force ;  yet  we  have  no  evidence  that  a  coat  of  armour  like 
that  of  the  tortoise  can  be  so  produced.  Nor,  indeed,  are  the 
conditions  under  which  only  its  production  in  such  a  man- 
ner could  be  accounted  for,  fulfilled ;  since  the  surface  of  the 
tortoise  is  not  exposed  to  greater  pressure  and  friction  than 
the  surfaces  of  other  creatures.  This  massive  carapace,  and 
the  strangely-adapted  osseous  frame-work  which  supports  it, 
are  unaccountable  as  results  of  evolution,  unless  through  the 
process  of  natural  selection.  Thus,  too,  is  it  with  the  pro- 
duction of  colours  in  birds  and  in  insects ;  the  formation  ol 
odoriferous  glands  in  mammals  ;  the  growth  of  such  excres- 
cences as  those  of  the  camel.  Thus,  in  short,  is  it  with  all 
those  organs  of  animals,  which  do  not  play  active  parts  in  the 
compound  rhythms  of  their  functions. 

Besides  giving  us  explanations  of  structural  characters 
that  are  otherwise  unaccountable,  Mr  Darwin  shows  how 
natural  selection  explains  peculiar  relations  between  indi- 
viduals in  certain  species.  Such  facts  as  the  dimorphism  of 
the  primrose  and  other  flowers,  he  proves  to  be  quite  in  har- 
mony with  his  hypothesis,  though  stumbling-blocks  to  all 


INDIRECT   EQUIL/BRAT10N.  449 

other  hypotheses.  "While  the  production  of  neuters  among 
bees  and  ants,  is  inexplicable  as  a  result  of  direct  adaptation, 
natural  selection  affords  a  feasible  solution  of  it.  The  various 
differences  that  accompany  difference  of  sex,  sometimes 
slight,  sometimes  very  great,  are  similarly  accounted  for. 
As  before  suggested  (§  79),  natural  selection  appears  capa- 
ble of  producing  and  maintaining  the  right  proportion  of 
the  sexes  in  each  species ;  and  it  requires  but  to  contemplate 
the  bearings  of  the  argument,  to  see  that  the  formation  of 
different  sexes  may  itself  have  been  determined  in  the  same 
way. 

To  convey  here  an  adequate  idea  of  Mr  Darwin's  doctrine, 
in  the  immense  range  of  its  applications,  is  of  course  impos- 
sible. The  few  illustrations  just  given,  serving  but  dimly  to 
indicate  the  many  classes  of  phenomena  interpreted  by  it, 
are  set  down  simply  to  remind  the  reader  what  Mr  Darwin's 
hypothesis  is,  and  what  are  the  else  insoluble  problems  which 
it  solves  for  us. 

§  1G6.  But  now,  though  it  seems  to  me  that  we  are  thus 
supplied  with  a  key  to  phenomena  which  are  multitudinous 
and  varied  beyond  all  conception  ;  it  also  seems  to  me  that 
there  is  a  moiety  of  the  phenomena  which  this  key  will  not 
unlock.  Mr  Darwin  himself  recognizes  use  and  disuse  of 
parts,  as  causes  of  modifications  in  organisms  ;  and  does  this, 
indeed,  to  a  greater  extent  than  do  some  who  accept  his 
general  conclusion.  But  I  conceive  that  he  does  not  re- 
cognize them  to  a  sufficient  extent.  "While  he  conclusively 
shows  that  tbe  inheritance  of  changes  of  structure,  caused  by 
changes  of  function,  is  utterly  insufficient  to  explain  a  great 
mass — probably  the  greater  mass — of  morphological  pheno- 
mena :  I  think  he  leaves  unconsidered  a  mass  of  morphological 
phenomena  that  are  explicable  as  results  of  functionally- 
acquired  modifications,  transmitted  and  increased,  and  which 
are  not  explicable  as  results  of  natural  selection. 

By  induction,  as  well  as  by  inference  from  the  hypothesis 


450  THE    EVOLUTION    OF   LLFE. 

of  natural  selection,  we  know  that  there  exists  a  balance 
among  the  powers  of  organs  which  habitually  act  together — 
such  proportions  among  them,  that  no  one  has  any  consider- 
able excess  of  efficiency.  We  see,  for  example,  that  through- 
out the  vascular  system,  there  is  maintained  an  equilibrium 
between  the  powers,  that  is,  the  developments,  of  the  com- 
ponent parts  :  in  some  cases,  under  excessive  exertion,  the 
heart  gives  way,  and  we  have  enlargement ;  in  other  cases 
the  large  arteries  give  way,  and  we  have  aneurisms ;  in  other 
cases  the  minute  blood-vessels  give  wray — now  bursting,  now 
becoming  chronically  congested.  That  is  to  say,  in  the 
average  constitution,  no  superfluous  strength  is  possessed 
by  any  of  the  appliances  for  circulating  the  blood.  Take, 
again,  a  set  of  motor  organs.  Great  strain  here  causes  the 
fibres  of  a  muscle  to  tear.  There  the  muscle  does  not  yield 
but  the  tendon  snaps.  Elsewhere  neither  muscle  nor  tendon 
is  damaged,  but  the  bone  breaks.  Joining  with  these  instances 
the  general  fact,  that  under  the  same  adverse  conditions, 
different  individuals  show  their  slight  differences  of  consti- 
tution by  going  wrong  some  in  one  way  and  some  in  an- 
other ;  and  that  even  in  the  same  individual,  similar  adverse 
conditions  will  now  affect  one  viscus  and  now  another ;  it 
becomes  manifest  that  though  there  cannot  be  maintained 
an  accurate  or  absolute  balance  among  the  powers  of  the 
organs  composing  an  organism,  yet  the  excesses  and  de- 
ficiencies of  power  are  extremely  slight.  That  they  must  be 
extremely  slight,  is,  as  before  said,  a  deduction  from  the 
hypothesis  of  natural  selection.  Mr  Darwin  himself  argues 
"  that  natural  selection  is  continually  trying  to  economize  hi 
every  part  of  the  organization.  If  under  changed  conditions 
of  life  a  structure  before  useful  becomes  less  useful,  any 
diminution,  however  slight,  in  its  development,  will  be  seized 
on  by  natural  selection,  for  it  will  profit  the  individual  not 
to  have  its  nutriment  wasted  in  building  up  an  useless  struc- 
ture." In  other  words,  if  any  muscle  has  more  fibres  than 
can  be  utilized,  or  if  a  bone  be  stronger  than  needful,  no  axl- 


INDIRECT    EQUILIBRATION.  461 

vantage  results,  but  rather  a  disadvantage — a  disadvantage 
which  will  decrease  the  chances  of  survival.  Hence 

it  becomes  a  corollary,  that  among  any  organs  which  habit- 
ually act  in  concert,  an  increase  of  one  can  be  of  no  service 
unless  there  is  a  concomitant  increase  of  the  rest.  The  co 
operative  parts  must  vary  together  ;  otherwise  variation  will 
be  detrimental.  A  stronger  muscle  must  have  a  stronger  bone 
to  resist  its  contractions;  must  have  stronger  correlated  mus- 
cles and  ligaments  to  secure  the  neighbouring  articulations  ; 
must  have  larger  blood-vessels  to  bring  it  supplies ;  must 
have  a  more  massive  nerve  to  bring  it  stimulus,  and  some 
extra  development  of  a  nervous  centre  to  supply  this  extra 
stimulus.  The  question  arises,  then, — does  spontaneous 
variation  occur  simultaneously  in  all  these  co-operative 
parts  ?  Have  we  any  reason  to  think  that  they  spontaneously 
increase  or  decrease  together  ?  The  assumption  that  they 
do,  seems  to  me  untenable  ;  and  its  untenability  will,  I  think, 
become  conspicuous  if  we  take  a  case,  and  observe  how  ex- 
tremely numerous  and  involved  are  the  variations  which 
must  be  supposed  to  occur  together.  In  illustration 

of  another  point,  we  have  already  considered  the  modifica- 
tion required  to  accompany  increased  weight  of  the  head. 
Instead  of  the  bison,  however,  the  moose  deer,  or  the  extinct 
Irish  elk,  will  here  best  serve  our  purpose.  In  this  species 
the  male  has  enormously-developed  horns,  which  are  used  for 
purposes  of  offence  and  defence.  These  horns,  weighing  up- 
wards of  a  hundred- weight,  are  carried  at  great  mechanical 
disadvantage — supported  as  they  are  along  with  the  massive 
skull  which  bears  them,  at  the  extremity  of  the  outstretched 
neck.  Further,  that  these  heavy  horns  may  be  of  use  in 
fighting,  the  supporting  bones  and  muscles  must  be  strong 
enough,  not  simply  to  carry  them,  but  to  put  them  in 
motion  with  the  rapidity  required  for  giving  blows.  Let  us, 
then,  ask  how,  by  natural  selection,  this  complex  apparatus 
of  bones  and  muscles  can  have  been  developed,  pari  passu 
with  the  horns  ?    If  we  suppose  the  horns  to  have  originally 


452  THE    EVOLUTION   OF    LIFE. 

been  of  like  size  with  those  borne  by  other  kinds  of  deer ; 
and  if  we  suppose  that  in  certain  individuals,  they  became 
larger  by  spontaneous  variation ;  what  would  be  the  con- 
comitant changes  required  to  render  their  greater  size  useful  ? 
Other  things  equal,  the  blow  given  by  a  larger  horn  woidd 
be  a  blow  given  by  a  heavier  mass  moving  at  a  smaller 
velocity :  the  momentum  would  be  the  same  as  before  ;  and 
the  area  of  contact  with  the  body  struck  being  somewhat 
increased,  while  the  velocity  was  decreased,  the  injury  done 
would  be  less.  That  the  horns  may  become  better  weapons, 
the  whole  apparatus  which  moves  them  must  be  so  strength- 
ened as  to  impress  more  force  on  them,  and  to  bear  the  more 
violent  reactions  of  the  blows  given.  The  bones  of  the  skull 
on  which  the  horns  are  seated  must  be  thickened ;  otherwise 
they  will  break.  To  render  the  thickening  of  these  bones 
advantageous,  the  vertebrae  of  the  neck  must  be  further  de- 
veloped ;  and  without  the  ligaments  that  hold  together  these 
vertebra?,  and  the  muscles  which  move  them,  are  also  enlarged^ 
nothing  will  be  gained.  Such  modifications  of  the  neck  will 
be  useless,  or  rather  will  be  detrimental,  if  its  fulcrum  be  noi 
made  capable  of  resisting  intenser  strains :  the  upper  dorsal 
vertebrae  and  their  spines  must  be  strengthened,  that  they 
may  withstand  the  more  violent  contractions  of  the  neck- 
muscles  ;  and  like  changes  must  be  made  on  the  scapular 
arch.  Still  more  must  there  be  required  a  simultaneous  de- 
velopment of  the  bones  and  muscles  of  the  fore-legs;  since 
each  of  these  extra  growths  in  the  horns,  in  the  skull,  in  the 
neck,  in  the  shoulders,  adds  to  the  burden  which  the  fore- 
legs have  to  bear ;  unless  this  deer  with  its  heavier  horns, 
head,  neck,  and  shoulders,  had  stronger  fore-legs,  it  would 
not  only  suffer  from  loss  of  speed  but  wovdd  even  fail  in  fight. 
Hence,  to  make  larger  horns  of  use,  additional  sizes  must  be 
acquired  by  numerous  bones,  muscles,  and  ligaments,  as  well 
as  by  the  blood-vessels  and  nerves  on  which  their  actions 
depend.  On  calling  to  mind  how  the  spraining  of  a  single 
small  muscle  in  the  foot,  incapacitates  for  walking,  or  how  a 


INDIRECT   EQUILIBRATION.  4G3 

permanent  weakness  in  one  of  its  ligaments  will  greatly 
diminish  the  power  of  a  limb,  it  will  be  seen  that  unless  all 
these  many  changes  are  simultaneously  made,  they  may  as 
well  be  none  of  them  made — or  rather,  they  had  better  be 
none  of  them  made  ;  since,  the  enlargements  of  some  parts, 
by  putting  greater  strains  on  connected  parts,  would  render 
them  relatively  weaker  if  they  remained  unenlarged.  Thus, 
then,  to  account  by  the  hypothesis  of  natural  selection,  for  such 
a  structure  as  that  of  the  moose  deer,  or  the  extinct  Irish  elk, 
we  must  suppose  a  spontaneous  increase  in  the  size  of  the 
horns,  to  be  accompanied  by  a  spontaneous  increase  in  each 
of  these  numerous  bones  and  muscles  and  ligaments  directly 
and  indirectly  implicated  in  the  use  of  the  horns.  Can  we 
with  any  propriety  do  this  ?  I  think  not.  It  would  be  a 
strong  supposition  that  the  vertebras  and  muscles  of  the  neck, 
spontaneously  enlarged  at  the  same  time  as  the  horns.  It 
would  be  a  still  stronger  supposition  that  the  upper  dorsal 
vertebrae  not  only  at  the  same  time  spontaneously  became 
more  massive,  but  also  spontaneously  altered  their  pro- 
portions in  appropriate  ways,  by  the  development  of  their 
immense  neural  spines.  And  it  would  be  an  assumption 
still  more  straining  our  powers  of  belief,  that  along  with 
heavier  horns  there  should  spontaneously  take  place  the  re- 
quired strengthenings  of  the  scapular  arch  and  the  fore-legs. 
Besides  the  multiplication  of  directly-cooperative  organs, 
the  multiplication  of  organs  that  do  not  cooperate,  save  in 
the  degree  implied  by  their  combination  in  the  same  organ- 
ism, seems  to  me  a  further  hindrance  to  the  development  of 
special  structures  by  natural  selection  alone.  Where  the  lifo 
is  comparatively  simple,  or  where  surrounding  circumstances 
render  some  one  function  supremely  important,  the  survival 
of  the  fittest  may  readily  bring  about  the  appropriate  struc- 
tural change,  without  any  aid  from  the  transmission  of  func- 
tionally-acquired modifications.  But  in  proportion  as  the 
life  grows  complex — in  proportion  as  a  healthy  existence 
cannot  be  secured  by  a  large  endowment  of  .come  one  power, 


454  T1IE    EVOLUTION    OF   LIFE. 

but  demands  many  powers  ;  in  the  same  -proportion  do  there 
arise  obstacles  to  the  increase  of  any  particular  power,  by 
"the  preservation  of  favoured  races  in  the  struggle  for 
life."  As  fast  as  the  faculties  are  multiplied,  so  fast  does  it 
become  possible  for  the  several  members  of  a  species  to  have 
various  kinds  of  superiorities  over  one  another.  While  one. 
saves  its  life  by  higher  speed,  another  does  the  like  by  clearer 
vision,  another  by  keener  scent,  another  by  quicker  hearing, 
another  by  greater  strength,  another  by  unusual  power  of 
enduring  cold  or  hunger,  another  by  special  sagacity,  another 
by  special  timidity,  another  by  special  courage ;  and  others  by 
other  bodily  and  mental  attributes.  Now  it  is  unquestionably 
true  that,  other  things  equal,  each  of  these  attributes,  giving 
its  possessor  an  extra  chance  of  life,  is  likely  to  be  transmitted 
to  posterity.  But  there  seems  no  reason  to  suppose  that  it  will 
be  increased  in  subsequent  generations  by  natural  selection. 
That  it  may  be  thus  increased,  the  individuals  not  possess- 
ing more  than  average  endowments  of  it,  must  be  more  fre- 
quently killed  off  than  individuals  highly  endowed  with  it ; 
and  this  can  happen  onty  when  the  attribute  is  one  of  greater 
importance,  for  the  time  being,  than  most  of  the  other  attri- 
butes. If  those  members  of  the  species  which  have  but 
ordinary  shares  of  it,  nevertheless  survive  by  virtue  of  other 
superiorities  which  they  severally  possess ;  then  it  is  not  easy 
to  see  how  this  particular  attribute  can  be  developed  by 
natural  selection  in  subsequent  generations.  The  probability 
seems  rather  to  be,  that  by  gamogenesis,  this  extra  endow- 
ment will,  on  the  average,  be  diminished  in  posterity — just 
serving  in  the  long  run  to  compensate  the  deficient  endow- 
ments of  other  individuals,  whose  special  powers  lie  in  other 
directions  ;  and  so  to  keep  up  the  normal  structure  of  the 
species.  The  working  out  of  the  process  is  here  somewhat 
difficult  to  follow ;  but  it  appears  to  me  that  as  fast  as  the 
number  of  bodily  and  mental  faculties  increases,  and  as  fast  as 
the  maintenance  of  life  comes  to  depend  less  on  the  amount 
of  any  one,  and  more  on  the  combined  action  of  all ;    so 


INDIRECT    EQUILIBRATION.  |.V, 

fast  does  the  production  of  specialities  of  character  by 
natural  selection  alone,  become  difficult.  Particularly  does 
this  seem  to  be  so  with  a  species  so  multitudinous  in  its 
powers  as  mankind ;  and  above  all  does  it  seem  to  be 
so  with  such  of  the  human  powers  as  have  but  minor  shares 
in  aiding  the  struggle  for  life — the  aesthetic  faculties,  for 
example. 

It  by  no  means  follows,  however,  that  in  cases  of  this  kind, 
and  cases  of  the  preceding  kind,  natural  selection  plays  no 
part.  Wherever  it  is  not  the  chief  agent  in  working  organic 
changes,  it  is  still,  very  generally,  a  secondary  agent.  The 
survival  of  the  fittest  must  nearly  always  further  the  produc- 
tion of  modifications  which  produce  fitness  ;  whether  they  be 
modifications  that  have  arisen  incidentally,  or  modifications 
that  have  been  caused  by  direct  adaptation.  Evidently,  those 
individuals  whose  constitutions  or  circumstances  have  facili- 
tated the  production  in  them  of  any  structural  change  con- 
sequent on  any  functional  change  demanded  by  some  new 
external  condition,  will  be  the  individuals  most  likely  to  live 
and  to  leave  descendants.  There  must  be  a  natural  selection 
of  functionally-acquired  peculiarities,  as  well  as  of  incidental 
peculiarities ;  and  hence  such  structural  changes  in  a  species 
as  result  from  changes  of  habit  necessitated  by  changed  cir- 
cumstances, natural  selection  will  render  more  rapid  than 
they  would  otherwise  be. 

There  are,  however,  some  modifications  in  the  sizes  and 
forms  of  parts,  which  cannot  have  been  aided  by  natural 
selection ;  but  which  must  have  resulted  wholly  from  the 
inheritance  of  functionally-produced  alterations.  The  dwind- 
ling away  of  organs  of  which  the  undue  sizes  entail  no 
appreciable  evils,  furnishes  the  best  evidence  of  this.  Take, 
for  an  example,  that  diminution  of  the  jaws  and  teeth  which 
characterizes  the  civilized  races,  as  contrasted  with  i\a 
savage  races.*     How  can  the  civilized  races  have  be?n  bene- 

*  I  am  indebted  to  Mr  Flower  for  the  opportunity  of  examining  the  collection 
of  6kullfl  in  the  Museum  of  the  College  of  Surgeons  for  verification  of  this.     V'i 


456  THE    EVOLUTION    OF    LIFE. 

6  ted  in  the  struggle  for  life,  by  the  slight  decrease  ia 
these  comparatively-small  bones  ?  No  functional  superiority 
possessed  by  a  small  jaw  over  a  large  jaw,  in  civilized  life, 
can  be  named  as  having  caused  the  more  frequent  survival 
of  small-jawed  individuals.  The  only  advantage  which 
smallness  of  jaw  might  be  supposed  to  give,  is  the  advantage 
of  economized  nutrition ;  and  this  could  not  be  great  enough 
to  further  the  preservation  of  men  possessing  it.  The  de- 
crease of  weight  in  the  jaw  and  co-operative  parts,  that  has 
arisen  in  the  course  of  many  thousands  of  years,  does  not 
amount  to  more  than  a  few  oimces.  This  decrease  has  to  be 
divided  among  the  many  generations  that  have  lived  and 
died  in  the  interval.  Let  us  admit  that  the  weight  of  these 
parts  diminished  to  the  extent  of  an  ounce  in  a  single  gener- 
ation (which  is  a  large  admission) ;  it  still  cannot  be  con- 
tended that  the  having  to  carry  an  ounce  less  in  weight,  or 
the  having  to  keep  in  repair  an  ounce  less  of  tissue,  could 
sensibly  affect  any  man's  fate.  And  if  it  never  did  this — 
nay,  if  it  did  not  cause  a,  frequent  survival  of  small-jawed  in- 
dividuals where  large-jaAved  individuals  died  ;  natural  selec- 
tion could  neither  cause  nor  aid  diminution  of  the  jaw  and 

fortunately  the  absence,  in  most  cases,  of  some  or  many  teeth,  prevented  me 
from  arriving  at  that  specific  result  which  would  have  been  given  by  weighing  a 
number  of  the  under  jaws  in  each  race.  Simple  inspection,  however,  disclosed 
a  sufficiently-conspicuous  difference.  The  under  jaws  of  Australians  and  Negroes, 
when  placed  side  by  side  with  those  of  Englishmen,  were  visibly  larger,  not  only 
relatively  but  absolutely.  One  Australian  jaw  only,  did  I  observe,  that  was  about 
of  the  same  actual  size  as  an  average  English  jaw  ;  and  this  (probably  the  jaw  of 
a  woman)  belonging  as  it  did  to  a  much  smaller  skull,  bore  a  much  greater  ratio 
to  the  whole  body  of  which  it  formed  part,  than  did  an  English  jaw  of  the  same 
actual  size.  In  all  the  other  cases,  the  under  jaws  of  these  inferior  races  (con- 
taining larger  teeth  than  our  own)  were  absolutely  more  massive  than  our  own- 
often  exceeding  them  in  all  dimensions  ;  and  relatively  to  the  smaller  skeletons 
of  these  inferior  races,  they  were  very  much  more  massive.  Let  me  add  that  the 
Aus'-ialian  and  Jvegro  jaws  are  thus  strongly  contrasted,  not  with  all  British  jaws, 
but  only  with  the  jaws  of  the  civilized  British.  An  ancient  British  skull  in  the 
collection,  possesses  a  jaw  almost  or  quite  as  massive  as  those  of  the  Australian 
skulls.  And  this  is  in  harmony  with  the  alleged  relation  between  greater  size  of 
jaws  and  greater  action  of  jaws,  involved  by  the  habits  of  savages. 


INDIRECT    EQLTLLU RATION.  4-07 

il&  appendages.  Here,  therefore,  the  decreased  action  of 
these  parts  which  has  accompanied  the  growth  of  civilized 
habits  (the  use  of  tools  and  the  disuse  of  coarse  food),  must 
have  been  the  sole  cause  at  work.  During  civilization  this 
decrease  of  function  has  affected,  more  or  less,  all  individuals. 
Through  direct  equilibration,  diminished  external  stress  on 
these  parts,  has  resulted  in  diminution  of  the  internal  forces 
by  which  this  stress  is  met.  From  generation  to  generation, 
this  lessening  of  the  parts  consequent  on  functional  decline 
has  been  inherited.  And  since  the  survival  of  individuals 
must  always  have  been  determined  by  more  important  struc- 
tural traits,  this  trait  can  have  neither  been  facilitated  nor 
retarded  by  natural  selection. 

5  167.  Returning:  from  these  extensive  classes  of  facts  for 
which  Mr  Darwin's  hypothesis  does  not  account,  to  the  still 
more  extensive  classes  of  facts  for  which  it  does  account,  and 
which  are  unaccountable  on  any  other  hypothesis ;  let  us 
consider  in  what  way  this  hypothesis  is  expressible  in  terms 
of  the  general  doctrine  of  evolution.  Already  it  has  been 
pointed  out  that  the  evolving  of  modified  types  by  "  natural 
selection  or  the  preservation  of  favoured  races  in  the  struggle 
for  life,"  must  be  a  process  of  equilibration,  since  it  residts 
in  the  production  of  organisms  that  are  in  equilibrium  with 
their  environments ;  and  at  the  outset  of  this  chapter,  some- 
thing was  done  towards  showing  how  this  continual  survival 
of  the  fittest,  may  be  understood  as  the  progressive  estab- 
lishment of  a  balance  between  inner  and  outer  forces.  Here, 
however,  we  must  consider  the  matter  more  closely.  It  re- 
mains to  be  shown  that  this  process  conforms  to  the  same 
o-cneral  mechanical  principles  as  do  all  other  equilibrations. 

On  previous  occasions  we  have  contemplated  the  assem- 
blage of  individuals  composing  a  species,  as  an  aggregate  in 
a  state  of  moving  equilibrium.  We  have  seen  that  its 
powers  of  multiplication  give  it  an  expansive  force  which  ia 
antagonized  by  other  forces ;  and  that  through  the  rhyth- 
SO 


458  TIl£    EVOLUTION    OF    LIFE. 

mical  variations  in  these  two  sets  of  forces,  there  is  main- 
tained an  oscillating  limit  to  its  habitat,  and  an  oscillating 
limit  to  its  numbers.  On  another  occasion  (§  96)  it  was 
shown  that  the  aggregate  of  individuals  constituting  a 
species,  has  a  kind  of  general  life,  which,  "  like  the  life  of  an 
individual,  is  maintained  by  the  unequal  and  ever- varying 
actions  of  incident  forces  on  its  different  parts."  We  saw 
that  "just  as,  in  each  organism,  incident  forces  constantly 
produce  divergences  from  the  mean  state  in  various  direc- 
tions, which  are  constantly  balanced  by  opposite  divergences 
indirectly  produced  by  other  incident  forces  ;  and  just  as  the 
combination  of  rhythmical  functions  thus  maintained,  con- 
stitutes the  life  of  the  organism ;  so,  in  a  species,  there  is 
through  gamogenesis  a  perpetual  neutralization  of  those  con- 
trary deviations  from  the  mean  state,  which  are  caused  in  its 
different  parts  by  different  sets  of  incident  forces  ;  and  it  is 
similarly  by  the  rhythmical  production  and  compensation  of 
these  contrary  deviations,  that  the  species  continues  to  live." 
Hence,  to  understand  the  way  in  which  a  species  is  affected  by 
causes  which  destroy  some  of  its  units  and  favour  the  multi- 
plication of  others,  we  must  consider  it  as  a  whole  whose  units 
are  held  together  by  complex  forces  that  are  ever  balancing 
themselves  and  ever  being  disturbed — a  whole  whose  moving 
equilibrium  is  continually  being  modified,  and  through 
which  waves  of  perturbation  are  continually  being  pro- 
pagated. Thus  much  premised,  let  us  next  call  to 
mind  in  what  way  moving  equilibria  in  general  are  changed. 
In  the  first  place,  the  necessary  effect  wrought  by  a  new  in- 
cident force  falling  on  any  part  of  an  aggregate  with  balanced 
motions,  is  to  produce  a  new  motion  in  the  direction  of  least 
resistance.  In  the  second  place,  the  new  incident  force  is 
gradually  used  up  in  overcoming  the  opposing  forces,  and 
when  it  is  all  expended  the  opposing  forces  produce  a  recoil 
— a  reverse  deviation  that  counter-balances  the  original  de- 
viation. Consequently,  to  consider  whether  the  moving  equi- 
librium of  a  species  is  modified  in  the  same  wav  as  moving 


INDIRECT    EQUILIBRATION.  459 

equilibria  in  general,  is  to  consider  whether,  when  exposed  tt 
a  new  force,  a  species  yields  in  the  direction  of  least  resist- 
ance ;  and  whether,  by  its  thus  yielding,  there  is  generated 
in  the  species  a  compensating  change  in  the  opposite  direc- 
tion.    "We  shall  find  that  it  does  both  these  things. 

For  what,  expressed  in  mechanical  terms,  is  the  effect 
wrought  on  a  species  by  some  previously-unknown  enemy, 
that  kills  such  of  its  members  as  fail  in  defending  them- 
selves ?  The  disappearance  of  those  individuals  which  meet 
the  destroying  forces  by  the  smallest  defensive  forces,  is  tan- 
tamount to  the  yielding  of  the  species  as  a  whole  at  the 
places  where  the  resistances  are  the  least.  Or  if  by  some 
general  influence,  such  as  alteration  of  climate,  the  members 
of  a  species  are  subject  to  any  increase  of  certain  external 
actions  that  are  ever  tending  to  overthrow  their  equilibria, 
and  which  they  are  ever  counter-balancing  by  the  absorp- 
tion of  nutriment,  which  are  the  first  to  die  ?  Those  that 
are  least  able  to  generate  the  internal  actions  which  antagon- 
ize these  external  actions.  If  the  change  be  an  increase  of 
the  winter's  cold,  then  such  members  of  the  species  as  have 
unusual  powers  of  getting  food  or  of  digesting  food,  or  such 
as  are  by  their  constitutional  aptitude  for  making  fat,  fur- 
nished with  reserve  stores  of  force,  available  in  times  of 
scarcity,  or  such  as  have  the  thickest  coats  and  so  lose  least 
heat  by  radiation,  survive ;  and  their  survival  implies  that 
in  each  of  them  the  moving  equilibrium  of  functions  presents 
such  an  adjustment  of  internal  forces,  as  prevents  its  over- 
throw by  the  modified  aggregate  of  external  forces.  Con- 
versely, the  members  that  die,  are,  other  things  equal,  those 
deficient  in  the  power  of  meeting  the  new  action  by  an  equi- 
valent counter-action.  Thus,  in  all  cases,  a  species  con- 
eidei'ed  as  an  aggregate  in  a  state  of  moving  equilibrium, 
has  its  state  changed  by  the  yielding  of  its  fluctuating 
mass  wherever  this  mass  is  weakest  in  the  relation  to  the 
special  forces  acting  on  it.  The  conclusion  is,  indeed,  a 
truism.  But  now,  what  must  follow  from  the  de- 


460  TIIE    EVOLUTION    OF    LITE. 

struction  of  the  least-resisting  individuals  and  survival  ci 
the  most-resisting  individuals  ?  On  the  moving  equilibrium 
of  the  species  as  a  whole,  existing  from  generation  to  gener- 
ation, the  effect  of  this  deviation  from  the  mean  state  is  to 
produce  a  compensating  deviation.  For  if  all  such  as  are  de- 
ficient of  power  in  a  certain  direction  are  destroyed,  what 
must  be  (he  influence  on  posterity  ?  Had  those  which  are 
destroyed  lived  and  left  offspring,  the  next  generation  would 
have  had  the  same  average  balance  of  powers  as  preceding 
generations  :  there  would  have  been  a  like  proportion  of  in- 
dividuals less  endowed  with  this  power,  and  individuals  more 
endowed  with  this  power.  But  the  more-endowed  individuals 
being  alone  left  to  continue  the  race,  there  must  result  a  new 
generation  characterized  by  a  larger  average  endowment  of 
this  power.  That  is  to  say,  on  the  moving  equilibrium  con- 
stituted by  a  species,  an  action  producing  change  in  a  given 
direction,  is  followed,  in  the  next  generation,  by  a  reaction 
producing  an  opposite  change.  Observe,  too,  that  these 
effects  correspond  in  their  degrees  of  violence.  If  the  altera- 
tion of  some  external  factor  is  so  great  that  it  leaves  alive 
only  a  few  individuals,  characterized  by  extreme  endowments 
of  the  power  required  to  antagonize  it ;  then,  in  succeeding 
generations,  there  is  a  rapid  multiplication  of  individuals 
similarly  characterized  by  extreme  endowments  of  this  power 
— the  force  impressed  calls  out  an  equivalent  conflicting 
force.  Moreover,  the  change  is  temporary  where  the  cause 
is  temporary,  and  permanent  where  the  cause  is  permanent. 
All  that  are  deficient  in  the  needful  attribute  having  been 
killed  off;  and  the  survivors  having  the  needful  attribute  in 
a  comparatively  high  degree ;  there  will  descend  from  thera, 
not  only  some  possessing  equal  amounts  of  this  attribute  with 
themselves,  but  also  some  possessing  less  amounts  of  it.  If 
the  agency  which  proves  fatal  to  them  has  not  continued  in 
action,  such  less-endowed  individuals  will  multiply ;  and  the 
species,  after  sundry  oscillations,  will  return  to  its  previous 
mean  state.    But  if  this  agency  be  a  persistent  one,  such  less 


INDIRECT    EQUILIBRATION.  461 

endowed  individuals  will  be  continually  killed  off;  and 
eventually  none  but  the  highly-endowed  individuals  will  be 
produced — a  new  moving  equilibrium,  adapted  to  the  new 
environing  conditions,  will  result. 

It  may  be  objected  that  this  mode  of  expressing  the  facts 
does  not  include  the  numerous  cases  in  which  a  species  be- 
comes modified  in  relation  to  surrounding  agencies  that 
do  not  actively  influence  it — cases  like  that  of  the  plant 
which  acquires  hooked  seed-vessels,  by  which  it  lays  hold  of 
the  skins  of  passing  animals,  and  makes  them  the  distributors 
of  its  seeds — cases  in  which  the  outer  agency  has  no  direct 
tendency  at  first  to  affect  the  species,  but  in  which  the  species 
so  alters  itself  as  to  take  advantage  of  the  outer  agency 
To  cases  of  this  kind,  however,  the  same  mode  of  inter 
pretation  applies  on  simply  changing  the  terms.  While,  in 
the  aggregate  of  influences  amid  which  a  species  exists,  there 
are  some  which  tend  to  overthrow  the  moving  equilibria  oi 
its  members,  there  are  others  which  facilitate  the  maintenance 
of  their  moving  equilibria,  and  some  which  are  capable  of 
giving  their  moving  equilibria  increased  stability :  instance 
the  spread  into  their  habitat  of  some  new  kind  of  prey,  which 
is  abundant  at  seasons  when  other  prey  is  scarce.  ISow  what 
is  the  process  by  which  the  moving  equilibrium  in  any 
species,  becomes  adapted  to  some  additional  external  factor 
which  furthers  its  maintenance  ?  Instead  of  an  increased 
resistance  to  be  met  and  counter-balanced,  there  is  here  a 
diminished  resistance ;  and  the  diminished  resistance  is 
equilibrated  in  the  same  way  as  the  increased  resistance.  As, 
in  the  one  case,  there  is  a  more  frequent  survival  of  those  in- 
dividuals whose  peculiarities  of  constitution  enable  them  best 
to  resist  the  new  adverse  factor  ;  so,  in  the  other  case,  there 
is  a  more  frequent  survival  of  individuals  whose  peculiarities 
of  constitution  enable  them  to  take  advantage  of  the  new 
favourable  factor.  In  each  member  of  the  species,  the  balance 
of  functions  and  correlated  arrangement  of  structures,  differ 
slightly  from  those  existing  in  other  members.     To  say  that 


462  THE    EVOLUTION    OF    LIFE. 

among  all  its  members,  one  is  better  adapted  than  the  rest  to 
take  advantage  of  some  before-nnused  agency  in  the  environ- 
ment, is  to  say  that  its  moving  equilibrium  is,  in  so  far,  more 
stably  adjusted  with  respect  to  the  aggregate  of  surrounding 
influences.  And  if,  as  a  consequence,  this  individual  main- 
tains its  moving  equilibrium  when  others  fail  to  do  so,  and 
produces  offspring  which  do  the  like — that  is,  if  individuals 
thus  characterized  multiply  and  supplant  the  rest ;  there  is 
evidently,  as  before,  a  process  by  which  an  equilibration  be- 
tween the  organism  and  its  environment  is  effected,  not  im- 
mediately but  mediately,  through  the  continuous  intercourse 
between  the  species  as  a  whole  and  the  environment. 

§  168.  Thus  we  see  that  indirect  equilibration  does  what- 
ever direct  equilibration  cannot  do.  It  is  scarcely  possible 
too  much  to  emphasize  the  conclusion,  that  all  these  processes 
by  which  organisms  are  re-fitted  to  their  ever-changing 
environments,  must  be  equilibrations  of  one  kind  or  other. 
As  authority  for  this  conclusion,  we  have  not  simply  the 
universal  truth  that  change  of  every  order  is  towards  equi- 
librium ;  but  we  have  also  the  truth  which  holds  throughout 
the  organic  world,  that  life  itself  is  the  maintenance  of  a  moving 
equilibrium  between  inner  and  outer  actions — the  continuous 
adjustment  of  internal  relations  to  external  relations;  or  the 
maintenance  of  a  correspondence  between  the  forces  to  which 
an  organism  is  subject  and  the  forces  which  it  evolves.  For 
if  the  preservation  of  life  is  the  preservation  of  such  a  moving 
equilibrium,  it  becomes  a  corollary  that  those  changes  which 
enable  a  species  to  live  under  altered  conditions,  are  changes 
towards  equilibrium  with  the  altered  conditions. 

Hence,  all  such  changes  being  equilibrations,  their  differ- 
ences can  be  nothing  but  differences  in  the  ways  through 
which  they  result.  If  they  are  not  effected  immediately, 
they  must  be  effected  mediately.  A  priori,  therefore,  we 
may  be  certain  that  all  processes  of  modification  which  do 


INDIRECT    EQUILIBRATION.  463 

not  come  within  the  class  of  direct  equilibrations,  must  come 
within  the  class  of  indirect  equilibrations. 

Examination  of  the  facts  confirms  this  conclusion.  Tho 
external  factors  to  which  a  species  is  exposed,  are  of  two 
kinds.  They  are  such  as  act  continuously  or  frequently  on  the 
individuals  ;  or  they  are  such  as  do  not  act  continuously  or 
frequently  on  the  individuals.  To  a  factor  which  continuously 
or  frequently  acts  on  the  individuals,  the  functions  of  the  in- 
dividuals re-adjust  themselves — there  is  direct  equilibration. 
While  a  factor  which  does  not  act  continuously  or-  fre- 
quently on  the  individuals,  acts  continuously  on  the  species  as 
a  whole — either  destroying  such  of  the  members  as  are  least 
capable  of  resisting  it,  or  fostering  such  of  the  members  as 
are  most  capable  of  taking  advantage  of  it.  And  by  the 
absti'action,  generation  after  generation,  of  those  least  in 
equilibrium  with  the  new  factor ;  or  by  the  extra  multipli- 
cation, generation  after  generation,  of  those  most  in  equi- 
librium with  the  new  factor ;  the  species  as  a  whole  is  event- 
ually brought  into  complete  equilibrium  with  the  new  factor 
— there  is  indirect  equilibration. 


CHAPTER   XIII. 

THE    CO-OPERATION    OF    THE    FACTORS. 

S  1C9.  Thus  the  phenomena  of  organic  evolution,  maj  be 
Interpreted  in  the  same  way  as  the  phenomena  of  all  other 
evolution.  Those  universal  laws  of  the  re- distribution  of 
matter  and  motion,  to  which  things  in  general  conform,  are 
conformed  to  by  all  living  things ;  whether  considered  in 
their  individual  histories,  in  their  histories  as  species,  or  in 
their  aggregate  history.  However  otherwise  they  may  ordin- 
arily be  expressed,  the  truths  of  development  as  exhibited  in 
the  animal  and  vegetal  kingdoms,  prove  to  be  expressible  as 
manifestations  of  those  abstract  truths  set  forth  in  First 
Principles.  Fully  to  see  this,  it  will  be  needful  for  us  to  con- 
template in  their  ensemble,  the  several  processes  separately 
described  in  the  four  preceding  chapters. 

If  the  forces  acting  on  any  aggregate  remain  the  same,  the 
changes  produced  by  them  in  the  aggregate  will  presently 
reach  a  limit,  at  which  the  constant  outer  forces  are  balanced 
by  the  constant  inner  forces  ;  and  thereafter  no  further  me- 
tamorphosis will  take  place.  Hence,  that  there  may  be 
continuous  changes  of  structure  in  organisms,  there  must  be 
continuous  changes  in  the  incident  forces.  This  condition  to 
the  evolution  of  animal  and  vegetal  forms,  we  find  to  be 
fully  satisfied.  The  astronomic,  geologic,  and  meteorologic 
changes  that  have  been  slowly  but  incessantly  going  on,  and 
have  been  increasing  iu  the  complexity  of  their  combinationn. 


THE    CO-OPERATION    OF    THE    FACTORS.  465 

have  been  perpetually  altering  the  circumstances  of  organ- 
isms ;  and  organisms,  as  they  have  become  more  numerous  in 
their  kinds'  and  higher  in  their  kinds,  have  been  perpetually 
altering  one  another's  circumstances.  Thus,  for  those  pro- 
gressive modifications  upon  modifications  which  organic  evo- 
lution implies,  we  find  a  sufficient  cause  in  the  modifications 
after  modifications,  which  every  environment  over  the  Earth's 
surface  has  been  undergoing,  throughout  all  geologic  and  pre- 
gcologic  times.  The  progressive  inner  changes  for 

which  we  thus  find  a  cause  in  the  continuous  outer  changes, 
conform,  eo  far  as  we  can  trace  them,  to  that  universal  law  of 
the  instability  of  the  homogeneous,  which  is  manifested 
throughout  evolution  in  general.  We  see  that  in  organisms, 
as  in  all  other  things,  the  exposure  of  different  parts  to 
different  kinds  and  amounts  of  incident  forces,  has  necessi- 
tated their  differentiation  ;  and  that  for  the  like  reason, 
aggregates  of  individuals  have  been  lapsing  into  varieties, 
and  species,  and  genera,  and  classes.  We  also  see  that  in 
each  type  of  organism,  as  in  the  aggregate  of  types,  the  mul- 
tiplication of  effects  has  continually  aided  this  transition  from 
a  more  homogeneous  to  a  more  heterogeneous  state.  And 
yet  again,  we  see  that  that  increasing  segregation,  and  con- 
comitant increasing  definiteness,  which  characterizes  the 
growing  heterogeneity  of  organisms,  has  been  insured  by  the 
necessary  maintenance  of  them  under  combinations  of  forces 
not  greatly  unlike  preceding  combinations — by  the  continual 
destruction  of  those  which  expose  themselves  to  aggregates 
of  external  actions  markedly  incongruous  with  the  aggregates 
of  their  internal  actions,  and  the  survival  of  those  subject 
only  to  comparatively  small  incongruities.  Finally, 

we  have  found  that  each  change  of  structure,  superposed  on 
preceding  changes,  has  been  a  re-equilibration  necessitated  by 
the  disturbance  of  a  preceding  equilibrium.  The  maintenance 
of  life  being  the  maintenance  of  a  balanced  combination  of 
functions,  it  follows  that  individuals  and  species  that  have 
continued  to  live,  are  individuals  and  species  in  which  the 


406  THE    EVOLT  TICN    OF    LIFE. 

balance  of  functions  Las  not  been  overthrown.  Inevitably, 
therefore,  survival  through  successive  changes  of  conditions, 
implies  successive  adjustments  of  the  balance  to  the  new  con- 
ditions. This  deduction  we  find  to  be  inductively  verified 
What  is  ordinarily  called  adaptation,  is,  when  translated  into 
mechanical  terms,  direct  equilibration.  And  that  process 
which,  under  the  name  of  natural  selection,  Mr  Darwin  has 
shown  to  be  an  ever-acting  means  of  fitting  the  structures  of 
organisms  to  their  circumstances,  we  find,  on  analysis,  to  be 
expressible  in  mechanical  terms  as  indirect  equilibration. 

The  actions  that  are  here  specified  in  succession,  are  in 
reality  simultaneous  ;  and  they  must  be  so  conceived  before 
organic  evolution  can  be  rightly  understood.  Some  aid 
towards  so  conceiving  them,  will  be  given  by  the  annexed 
table,  representing  the  co-operation  of  the  factors. 

§  170.  Respecting  this  co-operation  of  these  factors,  it  re- 
mains only  to  point  out  their  respective  shares  in  producing 
the  total  result ;  and  the  way  in  which  the  proportions  of 
their  respective  shares  vary  as  evolution  progresses. 

At  first,  changes  in  the  amounts  and  combinations  of  ex- 
ternal inorganic  forces,  astronomic,  geologic,  and  meteoro- 
logic,  were  the  only  causes  of  the  successive  modifications 
undergone  by  organisms ;  and  these  changes  have  continued, 
and  must  still  continue,  to  be  causes  of  such  modifications. 
As,  however,  through  the  diffusion  of  organisms,  and  the 
consequent  differential  actions  of  inorganic  forces  on  them, 
there  arose  unlikenesses  among  organisms,  producing  varieties, 
species,  genera,  orders,  classes,  &c. ;  the  actions  of  organisms 
on  one  another  became  new  sources  of  organic  modifications. 
And  as  fast  as  types  have  multiplied,  and  become  more  com- 
plex ;  so  fast  have  the  mutual  actions  of  organisms  come  to 
be  more  influential  factors  in  their  respective  evolutions. 
Until,  eventually,  as  we  see  exemplified  in  the  human  race, 
they  have  come  to  be  the  chief  factors. 

Passing  from  the  external  causes  of  change  to  the  internal 


THE    CO- OP?1, RATION    OF   THE    FACTORS. 


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468  THE    EVOLUTION   OF   LIFE. 

processes  of  change  entailed  by  them,  we  see  that  these,  too, 
have  varied  in  their  proportions — that  which  was  originally 
the  most  important  and  almost  the  sole  process,  becoming 
gradually  less  important,  if  not  at  last  the  least  important. 
Always  there  must  have  been,  and  always  there  must  con- 
tinue to  bo,  a  survival  of  the  fittest :  natural  selection  must 
have  been  in  operation  at  the  outset,  and  can  never  cease  to 
operate.  While  yet  organisms  had  comparatively  feeble 
powers  of  co-ordinating  their  actions,  and  adjusting  them  to 
environing  actions,  natural  selection  worked  almost  alone  in 
moulding  and  re-moulding  organisms  into  fitness  for  their 
changing  environments ;  and  natural  selection  has  re- 
mained almost  the  sole  agency  by  which  plants  and  in- 
ferior orders  of  animals  have  been  modified  and  developed 
The  equilibration  of  organisms  that  are  comparatively  passive, 
is  necessarily  effected  indirectly,  by  the  action  of  incident 
forces  on  the  species  as  a  whole.  But  along  with  the  gradual 
evolution  of  organisms  having  some  activity,  there  grows  up 
a  kind  of  equilibration  that  is  relatively  direct.  In  propor- 
tion as  the  activity  increases,  direct  equilibration  plays  a 
more  important  part.  Until,  when  the  nervo-muscular 
apparatus  becomes  greatly  developed,  and  the  power  of  vary- 
ing the  actions  to  fit  the  varying  requirements  becomes  con- 
siderable, the  share  taken  by  direct  equilibration  rises  into 
co-ordinate  importance.  "We  have  seen  reason  to  think  that 
as  fast  as  essential  faculties  multiply,  and  as  fast  as  the  num- 
ber of  organs  that  co-operate  in  any  given  function  increases, 
indirect  equilibration  through  natural  selection,  becomes  less 
and  less  capable  of  producing  specific  adaptations  ;  and  re- 
mains fully  capable  only  of  maintaining  the  general  fitness 
of  constitution  to  conditions.  Simultaneously,  the  production 
of  adaptations  by  direct  equili oration,  takes  the  first  place — 
indirect  equilibration  serving  to  facilitate  it.  Until  at  length, 
among  the  civilized  human  races,  the  equilibration  becomes 
mainly  direct :  the  action  of  natural  selection  being  restricted 
to  the  destruction  of  those  who  are  constitutionally  too  feeble 


THE    COOPERATION    OF   THE    FACTORS.  469 

to  live,  even  with  external  aid.  As  the  preservation  of  in- 
capables  is  habitually  secured  by  our  social  arrangements ; 
and  as  very  few  except  criminals  are  prevented  by  their  in- 
feriorities from  leaving  the  average  number  of  offspring  (in- 
deed the  balance  of  fertility  is  probably  in  favour  of  the  in- 
ferior) ;  it  results  that  survival  of  the  fittest,  can  scarcely  at 
all  act  in  such  way  as  to  produce  specialities  of  nature,  either 
bodily  or  mental.  Here  the  specialities  of  nature,  chiefly 
mental,  which  we  see  produced,  and  which  are  so  rapidly 
produced  that  a  few  centuries  show  a  considerable  change, 
must  be  ascribed  almost  wholly  to  direct  equilibration.* 

*  As  having  an  instructive  bearing  on  the  question  of  the  varieties  of  Man, 
let  me  here  refer  to  a  paper  on  "  The  Origin  of  the  Human  Races  "  read  before 
the  Anthropological  Society,  March  1st,  1864,  by  Mr  Alfred  Wallace— a  gentle- 
man well  known  among  naturalists,  as  having  independently  thought  out  the 
hypothesis  of  natural  selection,  though  at  a  later  date,  and  less  elaborately,  than 
Mr  Darwin.  In  this  paper,  Mr  Wallace  shows,  very  clearly  I  think,  that  along 
with  the  attainment  of  that  degree  of  intelligence  implied  by  the  use  of  imple- 
ments, clothing,  &c,  there  arises  a  tendency  for  modifications  of  brain  to  take  the 
place  of  modifications  of  body — still,  however,  regarding  the  natural  selection  of 
spontaneous  variations,  as  the  cause  of  the  modifications.  But  if  the  foregoing 
arguments  be  valid,  natural  selection  here  plays  but  the  secondary  part  of  fur- 
thering the  adaptations  otherwise  caused.  It  is  true  that,  as  Mr  Wallace  argues, 
and  as  I  have  myself  briefly  indicated  (see  Westminster  Review,  for  April,  1S"j_', 
pp.  4a6 — 501),  the  natural  selection  of  races,  leads  to  the  survival  of  the  more 
cerebrally-devcloped,  while  the  less  cerebrally-developcd  disappear.  But 
though  natural  selection  acts  freely  in  the  struggle  of  one  society  with  another ; 
yet,  among  the  units  of  each  society,  its  action  is  so  interfered  with,  that  there 
remains  no  adequate  cause  for  the  requirement  of  mental  superiority  by  one 
race  over  another,  except  the  inheritance  of  functionally-produced  modifica- 
tions. This  view,  however,  agrees  equally  well  with  Mr.  Wallace's  conclu- 
sion, that  at  a  certain  stage  of  evolution,  the  brain  begins  to  change  much 
more  than  the  body. 


CHAPTER   XIV. 

THE   CONVERGENCE   OF    THE    EVIDENCES. 

§  171.  Of  the  three  classes  of  evidences  that  have  "neon 
assigned,  the  a  priori,  which  we  took  first,  were  partly  nega- 
tive, partly  positive. 

On  considering  the  "  General  Aspects  of  the  Special-crea- 
tion-hypothesis," we  discovered  it  to  be  worthless.  Discredited 
by  its  origin,  and  wholly  without  any  basis  of  observed  fact, 
we  found  that  it  was  not  even  a  thinkable  hypothesis  ;  and 
while  thus  intellectually  illusive,  it  turned  out  on  examina- 
tion to  have  moral  implications  quite  at  variance  with  the 
professed  beliefs  of  those  who  hold  it. 

Contrariwise,  the  "  General  Aspects  of  the  Evolution-hy- 
pothesis," begot  the  stronger  faith  in  it  the  more  nearly  they 
were  considered.  By  its  lineage  and  its  kindred,  it  was 
found  to  be  as  closely  allied  with  the  proved  truths  of  modern 
science,  as  is  the  antagonist  hypothesis  with  the  proved 
errors  of  ancient  ignorance.  Instead  of  being  a  mere  pseud- 
idea,  we  saw  that  it  admitted  of  elaboration  into  a  definite 
conception — so  showing  its  legitimacy  as  an  hypothesis.  In- 
stead of  positing  a  purely  fictitious  process,  the  process  which 
it  alleges,  we  saw  to  be  one  that  is  actually  going  on  around 
us.  To  which  add,  that  morally  considered,  this  hypothesis 
presents  no  irreconcilable  incongruities. 

Thuy,  even  were  we  without   further  means  of  judging, 


THE   CONVERGENCE    OF   1HE    EVIDENCES.  471 

there  could  be  no  rational  hesitation  which  of  the  two  views 
6hould  be  entertained. 

§  172.  Further  means  of  judging,  however,  we  found  to 
be  afforded  by  bringing  the  two  hj'potheses  face  to  face  with 
the  general  truths  established  by  naturalists.  These  induct- 
ive evidences  were  dealt  with  in  four  chapters. 

"  The  Arguments  from  Classification  "  were  these.  Organ- 
isms fall  into  groups  within  groups  ;  and  this  is  the  arrange- 
ment which  we  see  results  from  evolution,  where  it  is  known 
to  take  place.  Of  these  groups  within  groups,  the  great  or 
primary  ones  are  the  most  unlike,  the  sub-groups  are  less 
unlike,  the  sub-sub-groups  still  less  iinlike,  and  so  on  ;  and 
this,  too,  is  a  characteristic  of  groups  demonstrably  produced 
by  evolution.  Moreover,  indefiniteness  of  equivalence  among 
the  groups,  is  common  to  those  which  we  know  have  been 
evolved,  and  those  here  supposed  to  have  been  evolved.  And 
then  there  is  the  further  significant  fact,  that  divergent 
groups  are  allied  through  their  lowest  rather  than  their 
highest  members — a  truth  which  the  hypothesis  of  evolution 
implies. 

Of  "the  Arguments  from  Embryology,"  the  first  and  most 
striking  is,  that  when  the  developments  of  embrj'os  are  traced 
from  their  common  starting  point,  and  their  divergences  and 
re-divergences  symbolized  by  a  genealogical  tree,  there  is 
manifest  a  general  parallelism  between  the  arrangement  of. 
its  primary,  secondary,  and  tertiary  branches,  and  the 
arrangement  of  the  divisions  and  sub-divisions  of  our  classi- 
fioations — a  general  parallelism  to  be  anticipated  as  a  result 
of  evolution.  Kor  do  those  minor  deviations  from  this 
general  parallelism,  which  at  first  sight  look  like  difficulties, 
fail,  on  closer  observation,  to  become  additional  supports ; 
since  those  traits  of  a  common  ancestry  which  embryology 
reveals,  arc,  if  modifications  have  resulted  from  changed  con- 
ditions, liable  to  be  distorted  or  disguised  in  quite  different 
ways  and  degrees  in  different  lines  of  descendants 


472  THE    EVOLUTION    OF   LIFE. 

We  next  considered  "the  Arguments  from  Morphology." 
Leaving  out  those  kinships  among  organisms  disclosed  by 
their  developmental  metamorphoses,  the  kinships  which  their 
adult  forms  show  are  profoundly  significant.  The  remarkable 
unities  of  type  which  are  found  under  such  different  exter- 
nals, are  inexplicable  except  as  results  of  community  of  de- 
scent with  non-community  of  modification.  Again,  each 
organism  analyzed  apart,  shows  us,  in  the  likenesses  obscured 
by  unlikenesses  of  its  component  parts,  a  peculiarity  of  struc- 
ture that  can  be  ascribed  only  to  the  formation  of  a  more 
heterogeneous  organism  out  of  a  more  homogeneous  one. 
And  once  more,  the  habitual  existence  of  rudimentary  organs, 
homologous  with  organs  that  are  developed  in  allied  animals 
or  plants,  while  it  admits  of  no  other  rational  interpretation, 
has  a  satisfactory  interpretation  given  to  it  by  the  hypo- 
thesis of  evolution. 

Last  of  the  inductive  evidences,  came  "  the  Arguments  from 
Distribution."  While  the  phenomena  of  distribution  in 
Space,  prove  to  be  unaccountable  as  results  of  designed  adapt- 
ation of  organisms  to  their  habitats,  they  prove  to  be 
accountable  as  results  of  the  competition  of  species,  and  the 
spread  of  the  superior  into  the  habitats  of  the  inferior,  fol- 
lowed by  the  changes  which  new  conditions  induce.  Though 
the  phenomena  of  distribution  in  Time,  are  so  fragmentary 
that  no  positive  conclusion  can  be  drawn  from  them ;  yet  all 
of  them  are  reconcileable  with  the  hypothesis  of  evolution,  and 
some  of  them  yield  it  strong  support — especially  the  near 
relationship  that  exists  between  the  living  and  extinct 
types  of  each  great  geographical  area. 

In  each  of  these  four  groups,  we  thus  found  several  argu- 
ments which  point  to  the  same  conclusion ;  and  the  con- 
clusion pointed  to  by  the  arguments  of  any  one  group,  is  that 
pointed  to  by  the  arguments  of  all  the  other  groups.  This 
coincidence  of  coincidences,  would  give  to  the  induction  a 
very  high  degree  of  probability,  even  were  it  not  enforced 
by  deduction. 


THE   CONVERGENCE    OF    THE    EVIDENCES.  473 

§  173.  But  the  conclusion  deductively  reached,  is  in  har- 
mony with  the  inductive  conclusion.  Passing  from  the  evi- 
dence that  evolution  has  taken  place,  to  the  question — How 
has  it  taken  place  ?  we  find  in  known  agencies  and  known 
processes,  adequate  causes  of  its  phenomena. 

In  astronomic,  geologic,  and  meteorologic  changes,  ever  in 
progress,  ever  combining  in  new  and  more  involved  ways, 
we  have  a  set  of  inorganic  factors  to  which  all  organisms  are 
exposed;  and  in  the  varying  and  complicating  actions  of 
organisms  on  one  another,  we  have  a  set  of  organic  factors 
that  alter  with  increasing  rapidity.  Thus,  speaking  gener- 
ally, all  members  of  the  Earth's  Flora  and  Fauna  are  con- 
tinually passing  into  new  environments — experience  per- 
petual re-arrangements  of  external  forces. 

Each  organic  aggregate,  whether  considered  individually 
or  as  a  continuously-existing  species,  is  modified  afresh  by 
each  fresh  distribution  of  external  forces.  To  its  pre-exist- 
ing differentiations,  new  differentiations  are  added ;  and  thus 
that  lapse  from  a  more  homogeneous  to  a  more  heterogeneous 
state,  which  would  have  a  fixed  limit  were  the  circumstances 
fixed,  has  its  limit  perpetually  removed  by  the  perpetual 
change  of  the  circumstances.  Meanwhile,  that  growing  com- 
plexity of  structure  thus  produced,  must,  in  the  average  of 
cases,  be  accompanied  by  an  increasing  definiteness  of  struc- 
ture ;  since  only  those  organisms  can  survive  which  subject 
themselves  to  aggregates  of  forces  that  are  not,  in  their  essen- 
tials, greatly  unlike  those  with  which  their  structures  cor- 
respond. And  at  the  same  time  that  progression  is  thus 
necessitated  as  a  general  result ;  yet,  as  change  of  structure 
arises  only  where  there  is  change  in  the  distribution  of  forces, 
it  will  not  take  place  in  organisms  which  elude  changes 
in  the  distribution  of  forces,  by  migration  or  otherwise. 

These   modifications  upon  modifications   which  result  in 
evolution  structurally   considered,   are  the  accompaniments 
of  those  functional  alterations  continually  required   to  re- 
equilibrate  inner   with   outer  actions.     That  moving  equi- 
31 


174  THE    EVOLUTION    OF    LIFE. 

Librium  of  inner  actions  corresponding  with  outer  actions, 
which  constitutes  the  life  of  an  organism,  must  either  be 
overthrown  by  a  change  in  the  outer  actions,  or  must  undergo 
perturbations  that  cannot  end  until  there  is  a  re-adjusted 
bain  nee  of  functions  and  correlative  adaptation  of  structures. 
Wherever  the  external  changes  are  such  as  to  be  continuously 
or  frequently  operative  on  individuals,  this  direct  equilibra- 
tion must  go  on. 

But  where  the  external  changes  are  either  such  as  are 
fatal  when  experienced  by  the  individuals,  or  such  as  act  on 
the  individuals  in  ways  that  do  not  affect  the  equilibrium  of 
their  functions ;  then  the  re-adjustment  results  through  the 
effects  produced  on  the  species  as  a  whole — there  is  indirect 
equilibration.  By  natural  selection  or  survival  cf  the  fittest 
— by  the  preservation  in  successive  generations  of  those 
whose  moving  equilibria  happen  to  be  least  at  variance  with 
the  requirements,  there  is  eventually  produced  a  changed 
equilibrium  completely  in  harmony  with  the  requirements. 

And  thus  it  results  that  those  universal  laws  of  the  re-dis- 
tribution of  matter  and  motion,  which  are  conformed  to  by 
evolution  in  general,  are  conformed  to  by  organic  evolution. 

§  174.  Even  were  this  the  whole  of  the  evidence  assign- 
able for  the  belief  that  organisms  of  all  orders  have  been 
gradually  evolved,  this  belief  would  have  a  warrant  much 
higher  than  that  of  very  many  belief's  that  are  regarded  aa 
established.  When  we  see  that  there  are  strong  a  priori  pro- 
babilities in  its  favour,  and  wholly  adverse  to  the  antagonist 
hypothesis — when  an  examination  of  the  facts  which  natural- 
ists have  accumulated,  leads  us  to  several  groups  of  inductions 
which  unite  in  supporting  it — and  when  the  characteristics 
which  conspire  to  show  that  organic  evolution  has  been  going 
on,  prove  to  be  deducible  from  those  universal  actions  known 
to  work  evolution  of  all  other  kinds ;  we  have  a  combination 
of  proofs  which  might  suffice  were  there  no  more  to  be  said. 

Bat  the  evidence  is  far  from  exhausted.     At  the  outset  of 


THE    CONVERGENCE    OF   THE   EVIDENCES.  475 

the  argument,  it  was  remarked  that  the  ensemble  of  vital 
phenomena  presented  by  the  organic  world  as  a  whole,  can- 
not be  properly  dealt  with  apart  from  tlie  ensemble  of  vital 
phenomena  presented  by  each  organism,  in  the  course  of  its 
growth,  development,  and  decay.  The  interpretation  of  either 
implies  interpretation  of  the  other  ;  since  the  two  are  in 
reality  parts  of  one  process.  Hence,  the  validity  of  any 
hypothesis  respecting  the  one  class  of  phenomena,  may  be 
tested  by  its  congruity  with  phenomena  of  the  other  class. 
We  are  now  about  to  pass  to  the  more  special  phenomena  of 
development,  as  displayed  in  the  structures  and  functions  of 
individual  organisms.  If  the  hypothesis  that  plants  and 
animals  have  been  progressively  evolved,  be  true,  it  must 
furnish  us  with  keys  to  these  phenomena.  We  shall  find  that 
it  does  this;  and  by  doing  it,  gives  numberless  additional 
vouchers  for  its  truth. 


APPENDIX 


[The  following  letter,  originally  written  for  publication  in  the  North 
American  Review,  but  declined  by  the  Editor  in  pursuance  of 
a  general  rule,  and  eventually  otherwise  published  in  the  United 
States,  I  have  thought  well  to  append  to  this  first  volume  of  the 
Principles  of  Biology.  /  do  this  because  the  questions  which  it 
discusses  are  dealt  with  in  this  volume ;  and  because  the  further  ex- 
planations it  furnishes  seem,  needful  to  prevent  misapprehensions.] 

ON    ALLEGED    "  SPONTANEOUS    GENERATION,"    AND    ON    THE 
HYPOTHESIS  OF  PHYSIOLOGICAL  UNITS. 

The  Editor  of    the  North  American   Review. 
Sir, 

It  is  in  most  cases  unwise  to  notice  adverse  criticisms. 
Either  they  do  not  admit  of  answers  or  the  answers  may  be  left  to 
the  penetration  of  readers.  When,  however,  a  critic's  allegations 
touch  the  fundamental  propositionsof  a  book,  and  especially  when  they 
appear  in  a  periodical  having  the  position  of  the  North  American 
Review,  the  case  is  altered.  For  these  reasons  the  article  on 
"  Philosophical  Biology,"  published  in  your  last  number,  demands 
from  me  an  attention  which  ordinary  criticisrjs  do  not. 

It  is  the  more  needful  for  mc  to  notice  ii,  because  its  two  leading 
objections  have  the  one  an  actual  fairness  and  the  other  an  apparaut 
fairness ;  and  in  the  absence  of  explanations  from  me,  they  will  be 
considered  as  substantiated  even  by  many,  or  perhaps  most,  of  those 
who  have  read  the  work  itself — much  more  by  those  who  have  not 
read  it.  That  to  prevent  the  spread  of  misapprehensions  I  ought  to 
say  something,  is  further  shown  by  the  fact  that  the  same  two  objec- 
tions have  already  been  made  in  England — the  one  by  Dr.  Child, 
of  Oxford,  in  his  Essays  on  Physiological  Subjects,  and  the  other  by 
a  writer  in  the  Westminster  Review  for  July,  18G5. 

In  the  note  to  which  your  reviewer  refers,  I  have,  as  he  says,  tacitly 
repudiated  the  belief  in  "spontaneous  generation;"  and  that  I  have 
done  this  in  such  a  way  as  to  leave  open  the  door  for  the  interpre- 
tation given  by  him  is  true.  Indeed  the  fact  that  Dr.  Child,  whose 
criticism  is  a  sympathetic  one,  puts  the  same  construction  on  this 
note,  proves  that  your  reviewer  has  but  drawn  what  seems  to  be  a 
necessary  inference.  Nevertheless,  the  inference  is  one  which  I  did 
not  intend  to  be  drawn. 

In  explanation,  let  me  at  the  outset  remark  that  I  am  placed  at  a 
disadvantage  in  having  had  to  omit  that  part  of  the  System  of 
Philosophy  which  deals  with  Inorganic  Evolution.  In  the  orginal 
programme  wili  be  found  a  parenthetic  reference  to  this  omitted 
part)  which  should,  as  there  stated,  precede  the  Principles  of  Biology. 


480 

Two  volumes  are  missing.  The  closing  chapter  of  the  second,  were 
it  written,  would  deal  with  the  evolution  of  organic  matter — the 
step  preceding  the  evolution  of  living  forms.  Habitually  carrying 
with  me  in  thought  the  contents  of  this  unwritten  chapter,  I  have, 
in  some  cases,  expressed  myself  as  though  the  reader  had  it  before 
him ;  and  have  thus  rendered  some  of  my  statements  liable  to 
misconstructions.  Apart  from  this,  however,  the  explanation  of  the 
apparent  inconsistency  is  very  simple,  if  not  very  obvious.  In  the  first 
place,  I  do  not  believe  in  the  "  spontaneous  generation"  commonly 
alleged,  and  referred  to  in  the  note ;  and  so  little  have  I  associated 
in  thought  this  alleged  "spontaneous  generation"  which  I  dis- 
believe, with  the  generation  by  evolution  which  I  do  believe,  that  the 
repudiation  of  the  one  never  occurred  to  me  as  liable  to  be  taken  for  re- 
pudiation of  the  other.  That  creatures  having  quite  specific  structures  are 
evolved  in  the  course  of  a  few  hours,  without  antecedents  calculated 
to  determine  their  specific  forms,  is  to  me  incredible.  Not  only  the 
established  truths  of  Biology,  but  the  established  truths  of  science 
in  general,  negative  the  supposition  that  organisms  having  struc- 
tures definite  enough  to  identify  them  as  belonging  to  known  genera 
and  species,  can  be  produced  in  the  absence  of  germs  derived  from 
antecedent  organisms  of  the  same  genera  and  species.  If  there  can 
suddenly  be  imposed  on  simple  protoplasm  the  organization  which 
constitutes  it  a  Paramecium,  I  see  no  reason  why  animals  of  greater 
complexity,  or  indeed  of  any  complexity,  may  not  be  constituted 
after  the  same  manner.  In  brief,  I  do  not  accept  these  alleged  facts 
as  exemplifying  Evolution,  because  they  imply  something  immensely 
beyond  that  which  Evolution,  as  I  understand  it,  can  achieve.  In 
the  second  place,  my  disbelief  extends  not  only  to  the  alleged  cases 
of  "  spontaneous  generation,"  but  to  every  case  akin  to  them.  The 
very  conception  of  spontaneity  is  wholly  incongruous  with  the  con- 
ception of  Evolution,  for  this  reason  1  regard  as  objectionable  Mr. 
Darwin's  phrase  "  spontaneous  variation  "  (as  indeed  he  does  himself) ; 
and  I  have  sought  to  show  that  there  are  always  assignable  causes  of 
variation.  No  form  of  Evolution,  inorganic  or  organic,  can  be 
spontaneous ;  but  in  every  instance  the  antecedent  forces  must  be 
adequate  in  their  quantities,  kinds,  and  distributions,  to  work  the 
observed  effects.  Neither  the  alleged  cases  of  "  spontaneous  gene- 
ration," nor  any  imaginable  cases  in  the  least  allied  to  them,  fulfil 
this  requirement. 

If,  accepting  these  alleged  cases  of  "  spontaneous  generation,"  I 
had  assumed,  as  your  reviewer  seems  to  do,  that  the  evolution  of 
organic  life  commenced  in  an  analogous  way  ;  then,  indeed,  I  should 
have  left  myself  open  to  a  fatal  criticism.  This  supposed  "  spon- 
taneous generation"  habitually  occurs  in  menstrua  that  contain 
either  organic  matter,  or  matter  originally  derived  from  organisms ; 
and  such  organic  matter,  proceeding  in  all  known  cases  from  organ- 
isms cf  a  higher  kind,  implies  the  pre-existence  of   such  highci 


481 

organisms.  By  what  kind  of  logic,  then,  is  it  inferrible  that 
organic  life  was  initiated  after  a  manner  like  that  in  which  Infusoria 
are  said  to  be  now  spontaneously  generated?  Where,  before  life 
commenced,  were  the  superior  organisms  from  which  these  lowest, 
organisms  obtained  their  organic  matter?  Without  doubting  that 
there  are  those  who,  as  the  reviewer  says,  "can  penetrate  deeper 
than  Mr.  Spencer  has  done  into  the  idea  of  universal  evolution," 
and  who.  as  he  contends,  prove  this_  by  accepting  the  doctrine  of 
"  spontaneous  generation"  ;  I  nevertheless  think  that  I  can  penetrate 
deep  enough  to  see  that  a  tenable  hypothesis  respecting  the  origin 
of  organic  life  must  be  reached  by  some  other  clue  than  that  fur- 
nished by  experiments  on  decoction  of  hay  and  extract  of  beef. 

From  what  I  do  not  believe,  let  me  now  pass  to  what  I  do  believe. 
Granting  that  the  formation  of  organic  matter,  and  the  evolution  of 
life  in  its  lowest  forms,  may  go  on  under  existing  cosmical  condi- 
tions; but  believing  it  more  likely  that  the  formation  of  such  matter 
and  such  forms,  took  place  at  a  time  when  the  heat  of  the  Earth's 
surface  was  falling  through  those  ranges  of  temperature  at  which 
the  higher  organic  compounds  are  unstable;  I  conceive  that  the 
moulding  of  such  organic  matter  into  the  simplest  types,  must  have 
commenced  with  portions  of  protoplasm  more  minute,  more  in- 
definite, and  more  inconstant  in  their  characters,  than  the  lowest 
Rhizopods — less  distinguishable  from  a  mere  fragment  of  albumen 
than  even  the  Protogenes  of  Professor  Haeckel.  The  evolution"  of 
specific  shapes  must,  like  all  other  organic  evolution,  have  resulted 
from  the  actions  and  reactions  between  such  incipient  types  and 
their  environments,  and  the  continued  survival  of  those  which  hap- 
pened to  have  specialities  best  fitted  to  the  specialities  of  their  en- 
vironments. To  reach  by  this  process  the  comparatively  well-spe- 
cialized forms  of  ordinary  Infusoria,  must,  I  conceive,  have  taken  an 
enormous  period  of  time. 

To  prevent,  as  far  as  may  be,  future  misapprehension,  let  me 
elaborate  this  conception  so  as  to  meet  the  particular  objections 
raised.  The  reviewer  takes  for  granted  that  a  "  first  organism  " 
must  be  assumed  by  me,  as  it  is  by  himself.  But  the  conception  of 
a  "  first  organism,"  in  anything  like  the  current  sense  of  the  words, 
is  wholly  at  variance  with  conception  of  evolution;  and  scarcely 
less  at  variance  with  the  facts  revealed  by  the  microscope.  The 
lowest  living  things  are  not  properly  speaking  organisms  at  all;  for 
they  have  no  distinctions  of  parts — no  traces  of  organization.  It  is 
almost  a  misuse  of  language  to  call  them  "  forms"  of  life:  not  only 
are  their  outlines,  when  distinguishable,  too  nnspecific  for  description, 
but  they  change  from  moment  to  moment  and  are  never  twice  alike, 
either  in  two  individuals  or  in  the  same  individual.  Even  the  word 
"type"  is  applicable  in  but  a  loose  way  ;  for  there  is  little  constancy 
in  their  generic  characters  :  according  as  the  surrounding  conditions 
determine,  they  undergo  transformations  now  of  one  kind  and  now  of 


482 

another.  And  the  vagueness,  the  inconstancy,  the  want  of  appre- 
ciable structure,  displayed  by  the  simplest  of  living  things  as  we 
now  see  them,  are  characters  (or  absences  of  characters)  which,  on 
the  hypothesis  of  Evolution,  must  have  been  still  more  decided 
when,  asat  first,  no  "  forms,"  no  "  types,"  no  "  specific  shapes,"  had 
been  moulded.  That  "  absolute  commencement  of  organic  life  on 
the  globe,"  which  the  reviewer  says  I  "  cannot  evade  the  admission 
of,"  I  distinctly  deny.  The  affirmation  of  universal  evolution  is  in 
itself  the  negation  of  an  "  absolute  commencement "  of  anything. 
Construed  in  terms  of  evolution,  every  kind  of  being  is  conceived  as 
a  product  of  modifications  wrought  by  insensible  gradations  on  a 
pre-existing  kind  of  being  ;  and  this  holds  as  fully  of  the  supposed 
"commencement  of  organic  life"  as  of  all  subsequent  developments 
of  organic  life.  It  is  no  more  needful  to  suppose  an  "  absolute 
commencement  of  organic  life "  or  a  "  first  organism,"  than  it  is 
needful  to  suppose  an  absolute  commencement  of  social  life  and  a 
first  social  organism.  The  assumption  of  such  a  necessity  in  this 
last  case,  made  by  early  speculators  with  their  theories  of  "  social 
contracts "  and  the  like,  is  disproved  by  the  facts ;  and  the  facts, 
so  far  as  they  are  ascertained,  disprove  the  assumption  of  such  a 
necessity  in  the  first  case.  That  organic  matter  was  not  produced 
all  at  once,  but  was  reached  through  steps,  we  are  well  warranted 
in  believing  by  the  experiences  of  chemists.  Organic  matters  are 
produced  iu  the  laboratory  by  what  we  may  literally  call  artificial 
evolution.  Chemists  find  themselves  unable  to  form  these  complex 
combinations  directly  from  their  elements ;  but  they  succeed  in  form- 
ing them  indirectly,  by  successive  modifications  of  simpler  combina- 
tions. In  some  binary  compound,  one  element  of  which  is  present 
in  several  equivalents,  a  change  is  made  by  substituting  for  one  of 
these  equivalents  an  equivalent  of  some  other  element ;  so  producing 
a  ternary  compound.  Then  another  of  the  equivalents  is  replaced, 
and  so  on.  For  instance,  beginning  with  ammonia,  N  H3,  a  higher 
form  is  obtained  by  replacing  one  of  the  atoms  of  hydrogen 
by  an  atom  of  methyl,  so  producing  methjl-amine,  N  (C  H3  H2)  j 
and  then,  under  the  further  action  of  methyl,  ending  in  a 
further  substitution,  there  is  reached  the  still  more  compound  sub- 
stance dimethyl-amine,  N  (C  H„)  (C  H,)  H.  And  in  this  manner 
highly  complex  substances  are  eventually  built  up.  Another 
characteristic  of  their  method  is  no  less  significant.  Two  com- 
plex compounds  are  employed  to  generate,  by  their  action  upon 
one  another,  a  compound  of  still  greater  complexity :  different 
heterogeneous  molecules  of  one  stage,  become  parents  of  a  mole- 
cule a  stage  higher  in  heterogeneity.  Thus,  having  built  up  acetic 
acid  out  of  its  elements,  and  having  by  the  process  of  substitution  de- 
scribed above,  changed  the  acetic  acid  into  propionic  acid,  and  propi- 
onic into  butyric,  of  which  the  formula  is    <  ^  k  m  Q\  \  ' 


483 

this  complex  compound,  by  operating  on  anotner  complex 
compound,  such  as  the  dimethyl-aniine  named  above,  gene- 
rates one  of  still  greater  complexity,  butyrate  of  dimethyl-amine 

|  C  O  (H  0()C  Hj)  HjN  (C  n3>  (c  na)  II.  See,  then,  the 
remarkable  parallelism.  The  progress  towards  higher  types  of 
organic  molecules  is  effected  by  modifications  upon  modifications ; 
as  throughout  Evolution  in  general.  Each  of  these  modifications  is 
a  change  of  the  molecule  into  equilibrium  with  its  environment — an 
adaptation,  as  it  were,  to  new  surrounding  conditions  to  which  it  is 
subjected  ;  as  throughout  Evolution  in  general.  Larger,  or  more 
integrated,  aggregates  (for  compound  molecules  are  such)  arc 
successively  generated;  as  throughout  Evolution  in  general.  More 
complex  or  heterogeneous  aggregates  are  so  made  to  arise,  one  out 
of  another ;  as  throughout  Evolution  in  general.  A  geometrically- 
increasing  multitude  of  these  larger  and  more  complex  aggregates 
so  produced,  at  the  same  time  results  ;  as  throughout  Evolution  in 
general.  And  it  is  by  the  action  of  the  successively  higher  forms 
on  one  another,  joined  with  the  action  of  environing  conditions,  that 
the  highest  forms  are  reached  ;  as  throughout  Evolution  in  general. 
When  we  thus  see  the  identity  of  method  at  the  two  extremes 
— when  we  see  that  the  general  laws  of  evolution,  as  they  are  exem- 
plified in  known  organisms,  have  been  unconsciously  conformed  to 
by  chemists  in  the  artificial  evolution  of  organic  matter;  we  can 
scarcely  doubt  that  these  laws  were  conformed  to  in  the  natural 
evolution  of  organic  matter,  and  afterwards  in  the  evolution  of  the 
simplest  organic  forms.  In  the  early  world,  as  in  the  modern 
laboratory,  inferior  types  of  organic  substances,  by  their  mutual 
actions  under  fit  conditions,  evolved  the  superior  types  of  organic 
substances,  ending  in  organizable  protoplasm.  And  it  can  hardly 
be  doubted  that  the  shaping  of  organizable  protoplasm,  which  is  a 
substance  modifiable  in  multitudinous  ways  with  extreme  facility, 
went  on  after  the  same  manner.  As  I  learn  from  one  of  our 
first  chemists,  Prof.  Erankland,  protein  is  capable  of  existing 
under  probably  at  least  a  thousand  isomeric  forms ;  and,  as 
we  shall  presently  see,  it  is  capable  of  forming,  with  itself 
and  other  elements,  substances  yet  more  intricate  in  composi- 
tion, that  are  practically  infinite  in  their  varieties  of  kind. 
Exposed  to  those  innumerable  modifications  of  conditions  which 
the  Earth's  surface  afforded,   here   in  amount  of  light,   there  in 

amount  of  heat,  and  elsewhere  in  the  mineral  quality  of  its  aqu< 9 

medium,  this  extremely  changeable  substance  must  have  undergone 
now  one,  now  another,  of  its  countless  metamorphoses.  And  to  the 
mutual  influences  of  its  metamorphic  forms  under  favouring  con- 
ditions, we  may  ascribe  the  production  of  the  still  more  composite, 
still  more  sensitive,  still  more  variously-changeable  portions  of 
organic  matter,  which,  iu  masses  more  minute  and  simpler  thai. 


481 

existing  Protozoa,  displayed  actions  verging  little  by  little 
into  those  called  vital — actions  -which  protein  itself  exhibits  in  a 
certain  degree,  and  which  the  lowest  known  living  things  exhibit 
only  in  a  greater  degree.  Thus,  setting  out  with  inductions  from 
the  experiences  of  organic  chemists  at  the  one  extreme,  and 
with  inductions  from  the  observations  of  biologists  at  the  other 
extreme,  we  are  enabled  deductively  to  bridge  the  interval — ■ 
are  enabled  to  conceive  how  organic  compounds  were  evolved,  and 
how,  by  a  continuance  of  the  process,  the  nascent  life  displayed  in 
these  became  gradually  more  pronounced.  And  this  it  is  which 
has  to  be  explained,  and  which  the  alleged  cases  of  "  spontaneous 
generation  ".  would  not,  were  they  substantiated,  help  us  in  the  least 
to  explain. 

It  is  thus  manifest,  I  think,  that  I  have  not  fallen  into  the  alleged 
inconsistency.  Nevertheless,  I  admit  that  your  reviewer  was 
justified  in  inferring  this  inconsistency  ;  and  I  take  blame  to  mysolf 
for  not  having  seen  that  the  statement,  as  I  have  left  it,  is  opci  to 
misconstruction. 

I  pass  now  to  the  second  allegation — that  in  ascribing  to  certain 
specific  molecules,  which  I  have  called  "  physiological  uniTs "  the 
aptitude  to  build  themselves  into  the  structure  of  the  organism  to 
which  they  are  peculiar,  I  have  abandoned  my  own  principle,  f.nd 
have  assumed  something  beyond  the  re-distribution  of  MaUer  and 
Motion.  As  put  by  the  reviewer,  his  case  appears  to  be  well  made 
out ;  and  that  he  is  not  altogether  unwarranted  in  so  putting  it, 
may  be  admitted.  Nevertheless,  there  docs  not  in  reality  exist  the 
supposed  incongruity. 

Before  attempting  to  make  clear  the  adequacy  of  the  conception 
which  I  am  said  to  have  tacitly  abandoned  as  insufficient,  lot  me 
remove  that  excess  of  improbability  the  reviewer  gives  to  it,  t)y  the 
extremely-restricted  meaning  with  which  he  uses  the  word  mtcham- 
eal.     In  discussing  a  proposition  of  mine  he  says  : — 

"  He  then  cites  certain  remarks  of  Mr.  Paget  on  the  permanent  effects 
wrought  in  the  blood  by  the  poison  of  scarlatina  and  small-pox,  as  justify- 
ing the  belief  that  such  a  'power'  exists,  and  attributes  the  repair  of  a 
wasted  tissue  to  '  forces  analogous  to  those  by  which  a  crystal  reproduces 
its  lost  apex.'  (Neither  of  which  phenomeua,  however,  is  explicable  by 
mechanical  causes.)" 

Were  it  not  for  the  deliberation  with  which  this  last  statement  is 
made,  I  should  take  it  for  a  slip  of  the  pen.  As  it  is,  however,  I 
have  no  course  left  but  to  suppose  the  reviewer  unaware  of  the  fact 
that  molecular  actions  of  all  kinds  are  now  not  only  conceived  as 
mechanical  actions,  but  that  calculations  based  on  this  conception  of 
them,  bring  out  the  results  that  correspond  with  observation.  There 
is  no  kind  of  re-arrangement  among  molecules  (crystallization 
beint;    one)    which    the    modern    physicist    does    not   think    of, 


483 

Mid  correctly  reason  npon,  in  terms  of  forces  and  motions  like 
those  of  sensible  masses.  Polarity  is  regarded  as  a  resultant  of 
such  forces  and  motions  ;  and  when,  as  happens  in  many  cases, 
light  changes  the  molecular  structure  of  a  crystal,  and  alters  its 
.polarity,  it  does  this  by  impressing,  in  conformity  with  mechanical 
laws,  new  motions  on  the  constituent  molecules.  That  the  reviewer 
should  present  the  mechanical  conception  under  so  extremely  limited 
a  form,  is  the  more  surprising  to  me  because,  at  the  outset  of  the 
very  work  he  reviews,  1  have,  in  various  passages,  based  inferences 
on  those  immense  extensions  of  it  which  he  ignores  ;  indicating,  for 
example,  the  interpretation  it  yields  of  the  inorganic  chemical 
changes  effected  by  heat,  and  the  organic  chemical  changes  effected 
by  light  (Principles  of  Biology,  §  \o.) 

Premising,  then,  that  the  ordinary  idea  of  mechanical  action  must 
be  greatly  expanded,  let  us  enter  upon  the  question  at  issue — the 
sufficiency  of  the  hypothesis  that  the  structure  of  each  organism  is 
determined  by  the  polarities  of  the  special  molecules,  or  physiologi- 
cal units,  peculiar  to  it  as  a  species,  which  necessitate  tendencies 
towards  special  arrangements.  My  proposition  and  the  reviewer's 
criticism  upon  it,  will  be  most  conveniently  presented  if  I  quote  in 
full  a  passage  of  his  from  which  1  have  already  extracted  some  ex- 
pressions.    He  says  : — 

"It  will  be  noticed,  however,  that  Mr.  Spsncer  attributes  the  possession 
of  these  'tendencies,'  or  'proclivities,'  to  natural  inheritance  from 
ancestral  organisms ;  and  it  may  be  argued  that  he  thus  saves  the 
mechanist  theory  and  his  own  consistency  at  the  same  time,  inasmuch  as 
he  derives  even  the  'tendencies'  themselves  ultimately  from  the  environ- 
ment. To  this  we  reply,  that  Mr.  Spencer,  who  advocates  the  nebular 
hypothesis,  cannot  evade  the  admission  of  an  absolute  commencement  of 
organic  life  on  the  globe,  and  that  the  'formative  tendencies,' without 
which  he  cannot  explain  the  evolution  of  a  single  individual,  could  not 
have  been  inherited  by  the  first  organism.  Besides,  by  his  virtual  denial 
of  spontaneous  generation,  he  denies  that  the  first  organism  was  evolved 
out  of  the  inorganic  world,  and  thus  shuts  himself  off  from  the  argument 
(otherwise  plausible)  that  its  'tendencies'  were  ultimately  derived  fro  i 
the  environment." 

This  assertion  is  already  in  great  measure  disposed  of  by  what 
lias  been  said  above.  Holding  that,  though  not  "  spontaneously 
generated,"  those  minute  portions  of  protoplasm  which  first  dis- 
played b  the  feeblesjj  degree  that  changeability  taken  to  imply  life, 
were  evolved,  I  am  not  debarred  from  the  argument  that  the  '"ten- 
dencies" of  the  physiological  units  are  derived  from  the  inherited 
effects  of  environing  actions.  If 'the  conception  of  a  ':rirst  organ- 
ism "  were  a  necessary  one,  the  reviewer's  objection  would  bo  valid. 
If  there  were  an  "  absolute  commencement"  of  life,  a  definite  line 
parting  organic  matter  from  the  simplest  living  forms,  I  should  be 
placed  in  the  predicament  he  describes.  But  as  the  doctrine  of 
Evolution  itself  tacitly  negatives  any  such  distinct  separation  ;  and 
■ts  the  negation  is  the  moro  confirmed  by  the   facts   the  more  w« 


436 

know  of  thcra ;  I  do  not  feel  that  I  am  entangled  in  the  alleged 
difficulty.  My  reply  might  end  here ;  but  as  the  hypothesis  in  ques- 
tion is  one  not  easily  conceived,  and  very  apt  to  be  misunderstood, 
I  will  attempt  a  further  elucidation  of  it. 

Much  evidence  now  conspires  to  show  that  molecules  of  the  sub- 
stances we  call  elementary  are  in  reality  compound ;  and  that,  by 
the  combination  of  these  with  one  another,  and  re-combinations  of 
the  products,  there  are  formed  systems  of  systems  of  molecules,  un- 
imaginable in  their  complexity.  Step  by  step  as  the  aggregate 
molecules  so  resulting,  grow  larger  and  increase  in  heterogeneity, 
they  become  more  unstable,  more  readily  transformable  by  small 
forces,  more  capable  of  assuming  various  characters.  Those  com- 
posing organic  matter  transcend  all  others  in  size  and  intricacy  of 
structure ;  and  in  them  these  resulting  traits  reach  their  extreme. 
As  implied  by  its  name  protein,  the  essential  substance  of  which 
organisms  are  built,  is  remarkable  alike  for  the  variety  of  its  meta- 
morphoses and  the  facility  with  which  it  undergoes  them  :  it  changes 
from  one  to  another  of  its  thousand  isomeric  forms  on  the  slightest 
change  of  conditions.  Now  there  are  facts  warranting  the  belief 
that  though  these  multitudinous  isomeric  forms  of  protein  will  not 
unite  directly  with  one  another,  yet  they  admit  of  being  linked  to- 
gether by  other  elements  with  which  they  combine.  And  it  is 
very  significant  that  there  are  habitually  present  two  other  elements, 
sulphur  and  phosphorus,  which  have  quite  special  powers  of  holding 
together  many  equivalents — the  one  being  pentatomic  and  the  other 
hexatomic.  So  that  it  is  a  legitmate  supposition  (justified  by  analo- 
gies) that  an  atom  of  sulphur  may  be  a  bond  of  union  among  half- 
a-dozen  different  isomeric  forms  of  protein;  and  similarly  with  phos- 
phorus. A  moment's  thought  will  show  that,  setting  out  with  the 
thousand  isomeric  forms  of  protein,  this  makes  possible  a  number  of 
these  combinations  almost  passing  the  power  of  figures  to  express. 
Molecules  so  produced,  perhaps  exceeding  in  size  and  complexity 
those  of  protein  as  those  of  protein  exceed  those  of  inorganic  matter, 
may,  I  conceive,  be  the  special  units  belonging  to  special  kinds  of 
organisms.  By  their  constitution  they  must  have  a  plasticity,  or 
sensitiveness  to  modifying  forces,  far  beyond  that  of  protein ;  and 
bearing  in  mind  not  only  that  their  varieties  are  practically  infinite 
in  number,  but  that  closely  allied  forms  of  them,  chemically  in- 
different to  one  another  as  they  must  be,  may  coexist  in  the  same 
aggregate,  we  shall  see  that  they  are  fitted  for  entering  into  un- 
limited varieties  of  organic  structures. 

The  existence  of  such  physiological  units,  peculiar  to  each  species 
of  organism,  is  not  unaccounted  for.  They  are  evolved  simul- 
taneously with  the  evolution  of  the  organisms  they  compose — they 
differentiate  as  fast  as  these  organisms  differentiate;  and  are  made 
multitudinous  in  kind  by  the  same  actions  which  make  the  organism 
they  compose  multitudinous  in  kind.     This  conceptiou  is  clearly 


487 

representable  in  terms  of  the  mechanical  hypothesis.  Every 
physicist  will  endorse  the  proposition  that  in  each  aggregate  there 
tends  to  establish  itself  an  equilibrium  between  the  forces  exercised 
by  all  the  units  upon  each  and  by  each  upon  all.  Even  in  masses 
of  substance  so  rigid  as  iron  and  glass,  there  goes  on  a  molecular 
re-arrangement,  slow  or  rapid  according  as  circumstances  facilitate, 
which  ends  only  when  there  is  a  complete  balance  between  the  actions  of 
the  parts  on  the  whole  and  the  actions  of  the  whole  on  the  parts :  the 
implication  being  that  every  change  in  the  form  or  size  of  the  whole, 
necessitates  some  redistribution  of  the  parts.  And  though  in  cases 
like  these,  there  occurs  only  a  polar  re-arrangement  of  the  molecules, 
without  changes  in  the  molecules  themselves;  yet  where,  as  often 
happens,  there  is  a  passage  from  the  colloid  to  the  crystalloid  state, 
a  change  of  constitution  occurs  in  the  molecules  themselves.  These 
truths  are  not  limited  to  inorganic  matter:  they  unquestionably 
hold  of  organic  matter.  As  certainly  as  molecules  of  alum  have  a 
form  of  equilibrium,  the  octahedron,  into  which  they  fall  when  the 
temperature  of  their  solvent  allows  them  to  aggregate,  so  certainly 
must  organic  molecules  of  each  kind,  no  matter  how  complex,  have 
a  form  of  equilibrium  in  which,  when  they  aggregate,  their  complex 
forces  are  balanced — a  form  far  less  rigid  and  definite,  for  the 
reason  that  they  have  far  less  definite  polarities,  are  far  more  un- 
stable, and  have  their  tendencies  more  easily  modified  by  environing 
conditions.  Equally  certain  is  it  that  the  special  molecules  having 
a  special  organic  structure  as  their  form  of  equilibrium,  must  be 
reacted  upon  by  the  total  forces  of  this  organic  structure ;  and  that, 
if  environing  actions  lead  to  any  change  in  this  organic  structure, 
these  special  molecules,  or  physiological  units,  subject  to  a  changed 
distribution  of  the  total  forces  acting  upon  them  will  undergo 
modification — modification  which  their  extreme  plasticity  will 
render  easy.  By  this  action  and  reaction  I  conceive  the  physio- 
logical units  peculiar  to  each  kind  of  organism,  to  have  been 
moulded  along  with  the  organism  itself.  betting  out  with 
the  stage  in  which  protein  in  minute  aggregates,  took  on 
those  simplest  differentiations  which  fitted  it  for  differently- 
conditioned  parts  of  its  medium,  there  must  have  unceasingly 
gone  on  perpetual  re-adjustments  of  balance  between  aggregates 
and  their  units — actions  and  reactions  of  the  two,  in  which  the 
units  tended  ever  to  establish  the  typical  form  produced  by  actions 
and  reactions  in  all  antecedent  generations,  while  the  aggregate,  if 
changed  in  form  by  change  of  surrounding  conditions,  tended  ever 
to  impress  on  the  units  a  corresponding  change  of  polarity,  causing 
them  in  the  next  generation  to  reproduce  the  changed  form — their 
uew  form  of  equilibrium. 

This  is  the  conception  which  I  have  sought  to  convey,  thou;,  h 
it  seems  unsuccessfully,  in  the  Principles  of  Biology ;  and  which  I 
have  there  used  to  interpret  the   many  involved   and   mysterionf 


488 

phenomena  of  Genesis,  Heredity,  and  Variation.  In  one  respect 
only  am  I  conscious  of  having  so  inadequately  explained  myself, 
as  to  give  occasion  for  a  misinterpretation — the  one  made  by 
the  Westminster  reviewer  above  referred  to.  By  him,  as  by  your 
own  critic,  it  is  alleged  that  in  the  idea  of  "  inherent  tendencies  " 
I  have  introduced,  under  a  disguise,  the  conception  of  "  the 
archseus,  vital  principle,  nisus  formativus,  and  so  on."  This 
allegation  is  in  part  answered  by  the  foregoing  explanation. 
That  which  I  have  here  to  add,  and  did  not  adequately  ex- 
plain in  the  Principles  of  Biology,  is  that  the  proclivity  of  units 
of  each  order  towards  the  specific  arrangement  seen  in  the 
organism  they  form,  is  not  to  be  understood  as  resulting 
from  their  own  structures  and  actions  only ;  but  as  the  product 
of  these  and  the  environing  forces  to  which  they  are  exposed. 
Organic  evolution  takes  place  only  on  condition  that  the  masses  of 
protoplasm  formed  of  the  physiological  units,  and  of  the  assimilable 
materials  out  of  which  others  like  themselves  are  to  be  multiplied, 
are  subject  to  heat  of  a  given  degree — are  subject,  that  is,  to  the 
unceasing  impacts  of  undulations  of  a  certain  strength  and  period ; 
and,  within  limits,  the  rapidity  with  which  the  physiological  units 
pass  from  their  indefinite  arrangement  to  the  detinite  arrangement 
they  presently  assume,  is  proportionate  to  the  strengths  of  the 
etherial  undulations  falling  upon  them.  In  its  complete  form,  then, 
the  conception  is  that  these  specific  molecules,  having  the  immense 
complexity  above  described,  and  having  correspondent^  complex 
polarities  which  cannot  be  mutually  balanced  by  any  simple  form 
of  aggregation,  have,  for  the  form  of  aggregation  in  which 
all  their  forces  are  equilibrated,  the  structure  of  the  adult 
organism  to  which  they  belong ;  and  that  they  are  compelled 
to  fall  into  this  structure  by  the  co-operation  of  the  en- 
vironing forces  acting  on  them,  and  the  forces  they  exercise  on  one 
another — the  environing  forces  being  the  source  of  the  power  which 
effects  the  re-arrangement,  and  the  polarities  of  the  molecules  deter- 
mining the  direction  in  which  that  power  is  turned.  Into  this  con- 
ception there  enters  no  trace  of  the  hypothesis  of  an  "  archseus  or 
vital  principle;"  and  the  principles  of  molecular  physics  fully  justify  it. 
It  is,  however,  objected  that  "the  living  body  in  its  develop- 
ment presents  a  long  succession  of  differing  forms  ;  a  continued 
series  of  changes  for  the  whole  length  of  which,  according  to  Mr. 
Spencer's  hypothesis,  the  physiological  units  must  have  an  'inherent 
tendency.'  Could  we  more  truly  say  of  anything,  'it  is  unrepresent- 
able in  thought  1 '"  I  reply  that  if  there  is  taken  into  account  an 
element  here  overlooked,  the  process  will  not  be  found  "  unrepre- 
sentable in  thought."  This  is  the  element  of  size  or  mass.  To 
satisfy  or  balance  the  polarities  of  each  order  of  physiological  units, 
not  only  a  certain  structure  of  organism,  but  a  certain  size  of 
organism  is  needed;  for  the  complexities  of  that  adult  struetnre 


489 

in  which  the  physiological  units  are  equilibrated,  cannot  be 
represented  within  the  small  bulk  of  the  embryo.  In  many 
minute  organisms,  where  the  whole  mass  of  physiological  units 
required  for  the  structure  is  present,  the  very  thing  does  take 
place  which  it  is  above  implied  ought  to  take  place.  The  mass 
builds  itself  directly  into  the  complete  form.  This  is  so  with 
Acari,  and  among  the  nematoid  Entozoa.  But  among  higher 
animals  such  direct  transformations  cannot  happen.  The  mass 
of  physiological  units  required  to  produce  the  size  as  well  as 
the  structure  that  approximately  equilibrates  them,  is  not  ail 
present,  but  has  to  be  formed  by  successive  additions — addi- 
tions which  in  viviparous  animals  are  made  by  absorbing, 
and  transforming  into  these  special  molecules,  the  organizable 
materials  directly  supplied  by  the  parent,  and  which  in  ovi- 
parous animals  are  made  by  doing  the  like  with  the  organ- 
izable materials  in  the  "  food-yelk,"'  deposited  by  the  parent  in  the 
same  envelope  with  the  germ.  Hence  it  results  that,  under  such 
conditions,  the  physiological  units  which  first  aggregate  into  the 
rudiment  of  the  future  organism,  do  not  form  a  structure  like  that 
of  the  adult  organism,  which,  when  of  such  small  dimensions,  does 
not  equilibrate  them.  They  distribute  themselves  so  as  partly  tu 
satisfy  the  chief  among  their  complex  polarities.  The  vaguely-dif- 
ferentiated mass  thus  produced  cannot,  however,  be  in  equilibrium. 
Each  increment  of  physiological  units  formed  and  integrated  by  it, 
changes  the  distribution  of  forces ;  and  this  has  a  double  effect.  It 
tends  to  modify  the  differentiations  already  made,  bringing  them  a 
step  nearer  to  the  equilibrating  structure;  and  the  physiological 
units  next  integrated,  being  brought  under  the  aggregate  of  polar 
forces  exercised  by  the  whole  mass,  which  now  approaches  a  step 
nearer  to  that  ultimate  distribution  of  polar  forces  which  exists  in 
the  adult  organism,  are  coerced  more  directly  into  the  typical  struc- 
ture. Thus  there  is  necessitated  a  series  of  compromises.  Each 
successive  form  assumed  is  unstable  and  transitional :  approach  to 
the  typical  structure  going  on  hand  in  hand  with  approach  to  the 
typical  bulk. 

Possibly  1  have  not  succeeded  by  this  explanation,  any  more  than 
by  the  original  explanation,  in  making  this  process  "  representable 
in  thought."  It  is  manifestly  untrue,  however,  that  I  have,  as 
alleged,  re-introduced  under  a  disguise  the  conception  of  a  "  vital 
principle."  That  I  interpret  embryonic  development  in  terms  of 
Mutter  and  Motion,  cannot,  I  think,  be  questioned.  Whether  the 
interpretation  is  adequate,  must  be  a  matter  of  opinion  ;  but  it  is 
clearly  a  matter  of  fact,  that  I  have  not  fallen  into  the  inconsistency 
asserted  by  your  reviewer.  At  the  same  time  1  willingly  admit  that, 
in  the  absence  of  certain  statements  which  I  have  now  supplied,  he 
was  not  unwarranted  in  representing  my  conception  in  the  way  thaf, 
he  has  done. 

32 


490 

But  while  I  consider  that  what  your  reviewer  has  said  on  these 
two  essential  points,  falls  within  the  limits  of  legitimate  criticism ;  I 
do  not  consider  that  he  is  justified  in  much  that  he  says  by  im- 
plication respecting  my  general  views. 

In  the  first  place,  he  conveys  a  totally  wrong  idea  of  the  mode 
of  interpretation  he  criticizes.  He  gives  his  readers  no  con- 
ception of  the  immense  extensions  which  modern  science  has  made 
of  the  "  mechanical  theory,"  now  applied  to  the  solution  of  all  phy- 
sical phenomena  whatever ;  but  he  has  deliberately  restricted  its  ap- 
plications in  a  way  that  produces  an  appearance  of  difficulty  where 
no  difficulty  exists.  The  common  uses  of  the  words  "  mechanical " 
and  "  mechanist,"  are  such  as  inevitably  call  up  in  all  minds  the 
notions  of  visible  masses  of  matter  acting  on  one  another  by  mea- 
surable forces  and  producing  sensible  motions.  In  the  absence  of 
explanations  or  illustrations  serving  to  enlarge  the  conception  thus 
suggested,  so  as  to  bring  within  it  the  oscillations  of  the  molecules 
of  matter,  and  the  undulations  of  the  molecules  of  ether  pervading 
all  space,  even  the  cultivated  reader  must  carry  with  him  an  ex- 
tremely crude  and  narrow  idea  of  the  "  mechanist  theory,"  and  can- 
not fail  to  be  struck  with  the  seeming  absurdity  of  interpreting  vital 
phenomena  in  mechanical  terms.  But  the  reviewer  says  nothing 
to  prevent  misconceptions  so  arising.  He  gives  no  hint  that  heat, 
light,  and  electricity,  are  now  all  recognized  as  "modes  of  mo- 
tion;" and  that  most  of  their  phenomena  are  mechanically  inter- 
preted, while  the  rest  are  regarded  as  mechanically  interpretable. 
He  does  not  explain  that  the  "mechanist"  theory  in  its  comprehen- 
sive form  embraces  actions  such  as  those  by  which  variations  in  the 
solar  spots  cause  variations  in  our  magnetic  needles,  and  actions  such 
as  those  through  which  Sirius  tells  us  what  substances  are  contained 
in  his  atmosphere.  True  he  makes  a  passing  reference  to  chemical 
changes  as  being  included  by  me  under  the  conception  of  mechanical; 
but  he  leaves  this  as  a  dead  statement  quite  unintelligible  to  the 
general  reader ;  and  in  the  typical  example  he  gives  of  my  mode  of  in- 
terpretation (the  development  of  vertebrae  by  transverse  strains)  he 
deliberately  excludes  the  physio-chemical  and  chemical  actions  which 
I  imply  as  co-operating,  and  describes  me  as  attributing  the  effects 
entirely  to  the  pressures  and  tensions  caused  by  muscular  move- 
ments !  (See  p.  408).  Instead  of  the  developed  ideas  of 
Matter  and  Motion  everywhere  implied  throughout  the  Principles 
of  Biology,  the  reviewer  leads  everyone  to  suppose  that  I  bring  to 
bear  on  biological  problems  nothing  beyond  the  vulgar  ideas  of 
Matter  and  Motion,  and  leaves  me  responsible  for  the  ludicrous 
incongruity ! 

That,  however,  which  I  regard  as  most  reprehensible  in  his  criti- 
cism is  the  way  in  which  he  persists  in  representing  the  System  of 
Philosophy  I  am  working  out  as  a  materialistic  system.  Already  he 
has  once  before  so  represented  it,  and  the  injustice  of  so  represent- 


491 

nig  It  lias  been  pointed  ont.  He  knows  that  I  have  repeatedly  and 
emphatically  asserted  that  our  conceptions  of  Matter  and  Motion 
are  but  symbols  of  an  Unknowable  Reality  ;  that  this  Reality  cannot 
be  that  which  we  symbolize  it  to  be ;  and  that  as  manifested  beyond 
consciousness  under  the  forms  of  Matter  and  Motion,  it  is  the  same 
as  that  which,  in  consciousness, is  manifested  as  Feeling  and  Thought. 
Yet  he  continues  to  describe  me  as  reducing  everything  to  dead 
mechanism.  If  his  statement  on  pp.  383-4  has  any  meaning  at  all, 
it  means  that  there  exists  some  "force  operating  ab  extra"  some 
"  external  power  "  distinguished  by  him  as  "  mechanical,"  which  is 
not  included  in  that  immanent  force  of  which  the  universe  is  a  mani- 
festation; though  whence  it  comes  he  does  not  tell  us.  This  con- 
ception he  speaks  of  as  though  it  were  mine ;  making  it  seem  that  I 
ascribe  the  moulding  of  organisms  to  the  actiou  of  this  "  mechani- 
cal "  "  external  power,"  which  is  distinct  from  the  Inscrutable  Cause 
of  things.  Yet  he  either  knows,  or  has  ample  means  of  knowing,  that 
I  deny  every  such  second  cause  :  indeed  he  has  himself  classed  me  as 
an  opponent  of  dualism.  I  recognize  no  forces  within  the  organism, 
or  without  the  organism,  but  the  variously-conditioned  modes  of  the 
universal  immanent  force ;  and  the  whole  process  of  organic  evolu- 
tion is  everywhere  attributed  by  me  to  the  co-operation  of  its  vari- 
ously-conditioned modes,  internal  and  external.  That  this  has  been 
all  along  my  general  view,  is  clearly  shown  in  the  closing  paragraph 
of  First  Principles,  where  I  have  said — 

"A  Power  of  which  the  nature  remains  for  ever  inconceivable,  and 
to  which  no  limits  in  Time  or  Space  can  be  imagined,  works  in  us  certain 
effects.  These  effects  have  certain  likenesses  of  kind,  the  most  general  of 
which  we  class  together  under  the  names  of  Matter,  Motion,  and  Force  ; 
and  between  these  effects  there  are  likenesses  of  connection,  the  most 
constant  of  which  we  class  as  laws  of  the  highest  certainty.  Analysis 
reduces  these  several  kinds  of  effect  to  one  kind  of  effect ;  and  these 
several  kinds  of  uniformity  to  one  kind  of  uniformity.  And  the  highest 
achievement  of  Science  is  the  interpretation  of  all  orders  of  phenomena, 
as  differently-conditioned  manifestations  of  this  one  kind  of  elfect,  under 
differently-conditioned  modes  of  this  one  kind  of  uniformity.  But  when 
Science  has  done  this,  it  has  done  nothing  more  than  systematize  our 
experience  ;  and  has  in  no  degree  extended  the  limits  of  our  experience. 
We  can  say  no  more  than  before,  whether  the  uniformities  are  as 
absolutely  necessary,  as  they  have  become  to  our  thought  relatively 
necessary.  The  utmost  possibility  for  us,  is  an  interpretation  of  the 
process  of  things  as  it  presents  itself  to  our  limited  consciousness;  but 
now  this  process  is  related  to  the  actual  process,  we  are  unable  to 
conceive,  much  less  to  know.  Similarly,  it  must  be  remembered 

that  while  the  connection  between  the  phenomenal  order  and  the 
ontological  order  is  for  ever  inscrutable  ;  so  is  the  connection  between  the 
conditioned  forms  of  being  and  the  unconditioned  form  of  being  for 
ever  inscrutable.  The  interpretation  of  all  phenomena  in  terms  of  Matter, 
Motion,  and  Force,  is  nothing  more  than  the  reduction  of  our  complex 
6ymbols  of  thought,  to  the  simplest  symbols;  and  when  the  equation  has 
been  brought  to  its  lowest  terms  the  symbols  remain  symbols  still.  Hence 
the  reasonings  contained  in  the  foregoing  pages,  afford  no  support  to 
either  of   the    antagonist   hypotheses    respecting  the    ultimate  nature  of 


492 

things.  Their  implications  are  no  more  matenalistio  than  they  are 
spiritualistic  ;  and  no  more  spiritualistic  than  they  are  materialistic. 
Any  argument  which  is  apparently  furnished  to  either  hypothesis,  is 
neutralized  by  as  good  an  argument  furnished  to  the  other.  The 
Materialist,  seeing  it  to  be  a  necessary  deduction  from  the  law  of  correla- 
tion, that  what  exists  in  consciousness  under  the  form  of  feeling,  is 
transformable  into  an  equivalent  of  mechanical  motion,  and  by 
consequence  into  equivalents  of  all  the  other  forces  which  matter 
exhibits  ;  may  consider  it  therefore  demonstrated  that  the  phenomena  of 
consciousness  are  material  phenomena.  But  the  Spiritualist,  setting  out 
with  the  same  data,  may  argue  with  equal  cogency,  that  if  the  forces 
displayed  by  matter  are  cognizable  only  under  the  shape  of  those 
equivalent  amounts  of  consciousness  which  they  produce,  it  is  to  be 
inferred  tbat  these  forces,  when  existing  out  of  consciousness,  are  of  the 
same  intrinsic  nature  as  when  existing  in  consciousness  ;  and  that  so  is 
justified  the  spiritualistic  conception  of  the  external  world,  as  consisting  of 
something  essentially  identical  with  what  we  call  mind.  Manifestly,  the 
establishment  of  correlation  and  equivalence  between  the  forces  of  the  outer 
and  the  inner  worlds,  may  be  used  to  assimilate  either  to  the  other  ;  ac- 
cording as  we  set  out  with  one  or  other  term.  But  he  who  rightly  inter- 
prets the  doctrine  contained  in  this  work,  will  see  that  neither  of  these 
terms  can  be  taken  as  ultimate.  He  will  see  that  though  the  relation  of 
subject  and  object  renders  necessary  to  us  these  antithetical  conceptions  of 
Spirit  and  Matter  ;  the  one  is  no  less  than  the  other  to  be  regarded  as  but 
a  sign  of  the  Unknown  Reality  which  underlies  both." 

This  is  the  conception  which  your  reviewer  continues  to  speak 
of  as  "  mechanical "  and  "  mechanist ;"  without  giving  his  reade-  s 
any  suspicion  of  the  qualified  sense  in  which  only  these  words  can 
be  applied.  If  he  thinks  that  by  doing  this  he  has  represented  the 
conception  with  fairness,  or  with  any  approach  to  fairness,  I  cannot, 
agree  with  him. 

I  am,  Sir, 

Yours,  &c, 

HERBERT  SPENCER. 
London,  December  5,  1868. 


rxonm  usiurt 
N.  C.  State  College 


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